Quartz crystal unit and method for manufacturing a quartz crystal unit and electronic apparatus

ABSTRACT

A method for manufacturing a quartz crystal unit comprises forming a quartz crystal tuning fork resonator that is capable of vibrating in a flexural mode of an inverse phase and that has a quartz crystal tuning fork base, and first and second quartz crystal tuning fork tines connected to the quartz crystal tuning fork base. An electrode is disposed on each of two of side surfaces of each of the first and second quartz crystal tuning fork tines so that the electrodes of the first quartz crystal tuning fork tine have an electrical polarity opposite to an electrical polarity of the electrodes of the second quartz crystal tuning fork tine, a motional capacitance C 1  of a fundamental mode of vibration of the quartz crystal tuning fork resonator being greater than a motional capacitance C 2  of a second overtone mode of vibration thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.11/511,679 filed Aug. 29, 2006 and now U.S. Pat. No. 7,528,682, which isa continuation-in-part of application Ser. No. 11/301,530 filed Dec 13,2005 and now U.S. Pat. No. 7,412,764, which is a continuation-in-part ofapplication Ser. No. 10/749,182 filed Dec. 30, 2003 and now U.S. Pat.No. 7,071,794, which is a continuation-in-part of application Ser. No.10/378,719 filed Mar. 4, 2003 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resonator, especially, a quartzcrystal resonator, a quartz crystal unit having the quartz crystalresonator, a quartz crystal oscillator having the quartz crystal unit,an electronic apparatus comprising a display portion and the quartzcrystal oscillator at least, and their manufacturing methods.

2. Background Information

There are many electronic apparatus comprising a display portion and aquartz crystal oscillator at least. For example, cellular phones,wristwatches, facsimiles and pagers comprising a quartz crystaloscillator are well known. Recently, because of high stability forfrequency, miniaturization and the light weight nature of theseelectronic apparatus, the need for an electronic apparatus comprising asmaller quartz crystal oscillator with a high frequency stability hasarisen. For example, the quartz crystal oscillator with a quartz crystaltuning fork resonator, which is capable of vibrating in a flexural mode,is widely used as a time standard in an electronic apparatus such as thecellular phones, the wristwatches, the facsimiles and the pagers.Similar to this, the same need has also arisen for an electronicapparatus comprising a length-extensional mode quartz crystal resonatorwith a frequency of 1 MHz to 10 MHz to decrease an electric currentconsumption of the electronic apparatus.

Heretofore, however, it has been impossible to obtain an electronicapparatus comprising a smaller quartz crystal oscillator with aconventional miniaturized quartz crystal tuning fork resonator, capableof vibrating in a flexural mode, and having a high frequency stability,a small series resistance and a high quality factor. When miniaturized,the conventional quartz crystal tuning fork resonator, capable ofvibrating in a flexural mode, as shown in FIG. 12 (which has electrodeson the obverse faces 203, 207, reverse faces 204, 208 and the four sides205, 206, 209, 210 of each tuning fork tine, as also shown in FIG. 13—across-sectional view of tuning fork tines of FIG. 12), it has a smallerelectromechanical transformation efficiency because the resonator shapeand the electrode construction provide a small electric field (i.e. Exbecomes small), as a result of which the resonator has a low frequencystability, a large series resistance and a reduced quality factor. InFIG. 12, a conventional tuning fork resonator 200 is shown with tines201, 202 and a base 230.

Moreover, for example, Japanese Patent Nos. P56-65517 and P2000-223992Aand International Patent No. WO 00/44092 were published and teachgrooves and electrodes constructed at tuning fork tines of a flexuralmode, tuning fork, quartz crystal resonator. However, they teach nothingabout a quartz crystal oscillator of the present invention having novelshape, novel electrode construction and figure of merit M for a quartzcrystal tuning fork resonator, capable of vibrating in a flexural modeand about a relationship of an amplification circuit and a feedbackcircuit which construct a quartz crystal oscillating circuit.

Additionally, for example, there has been a big problem in theconventional oscillator with the conventional quartz crystal tuning forkresonator, such that a fundamental mode vibration of the resonator jumpsto a second overtone mode vibration by shock or vibration.

Similarly, however, it has been impossible to obtain an electronicapparatus comprising a smaller quartz crystal oscillator with aconventional length-extensional mode quartz crystal resonator, capableof vibrating in a length-extensional mode, and having a frequency of 1MHz to 10 MHz, a small series resistance and a high quality factor. Asan example of a length-extensional mode quartz crystal resonator of theprior art, the length-extensional mode resonator comprising avibrational portion, connecting portions and supporting portions, whichis formed from a Z plate perpendicular to z axis, is well known, andthis resonator is formed integrally by a chemical etching process. Also,electrodes are disposed opposite each other on sides of the vibrationalportion formed by the chemical etching process so that the electrodesdisposed opposite each other are of opposite electrical polarity.

Also, a cutting angle of the conventional length-extensional mode quartzcrystal resonator is generally within a range of ZYw(0° to +5°),according to an IEEE notation. In detail, the connecting portions areconnected opposite each other at both end portions of a width of thevibrational portion and at a central portion of the length directionthereof. Namely, the direction of the connecting portions constructedopposite each other corresponds to the direction of the electric field.

When an alternating current (AC) voltage is applied between theelectrodes, an electric field occurs alternately in the width direction,as a result, the resonator is capable of vibrating in the lengthdirection, but the electric field of between the electrodes becomes verysmall because quartz crystal is an anisotropic material and the sides ofthe vibrational portion have a complicated shape formed by the chemicaletching process. Namely, the resonator has small electromechanicaltransformation efficiency because the resonator's shape and theelectrode construction provide a small electric field, consequently, theresonator has a low frequency stability, a large series resistance and areduced quality factor when it has the frequency of 1 MHz to 10 MHz.

It is, therefore, a general object of the present invention to provideembodiments of an electronic apparatus and a quartz crystal oscillator,which constructs an electronic apparatus of the present invention,comprising a quartz crystal oscillating circuit with a flexural mode,quartz crystal tuning fork resonator, capable of vibrating in afundamental mode, and having a high frequency stability, a small seriesresistance and a high quality factor, or embodiments of a quartz crystaloscillator, which also constructs an electronic apparatus of the presentinvention, comprising a quartz crystal oscillating circuit with alength-extensional mode quartz crystal resonator having a frequency of 1MHz to 10 MHz, a small series resistance and a high quality factor,which overcome or at least mitigate one or more of the above problems.

SUMMARY OF THE INVENTION

The present invention relates to a resonator, especially, a quartzcrystal resonator, a quartz crystal unit having the quartz crystalresonator, a quartz crystal oscillator having the quartz crystal unit,and an electronic apparatus comprising a display portion and the quartzcrystal oscillator at least, and their manufacturing methods, and moreespecially relates to the quartz crystal resonator which is a quartzcrystal tuning fork resonator capable of vibrating in a flexural mode ofan inverse phase, and having a groove and/or a through-hole at tuningfork tines, the quartz crystal unit having the quartz crystal tuningfork resonator, and the quartz crystal oscillator having the quartzcrystal unit. In detail, the quartz crystal oscillator comprises aquartz crystal oscillating circuit having an amplification circuit and afeedback circuit, and in particular, relates to a quartz crystaloscillator having a flexural mode, quartz crystal tuning fork resonatorcapable of vibrating in a fundamental mode and having an output signalof a high frequency stability for the fundamental mode vibration of theresonator, and also to a quartz crystal oscillator having a suppressedsecond overtone mode vibration of the flexural mode, quartz crystaltuning fork resonator, in addition, relates to a quartz crystaloscillator comprising a length-extensional mode quartz crystalresonator. The quartz crystal oscillators are, therefore, available forthe electronic apparatus requiring miniaturized and low priced quartzcrystal oscillators with high time accuracy and shock proof.

It is an object of the present invention to provide an electronicapparatus comprising a quartz crystal oscillator with a miniature quartzcrystal tuning fork resonator, capable of vibrating in a flexural mode,and having a high frequency stability, a small series resistance R₁ anda high quality factor Q₁, whose nominal frequency for a fundamental modevibration is within a range of 10 kHz to 200 kHz.

It is an another object of the present invention to provide anelectronic apparatus comprising a quartz crystal oscillator with aflexural mode, quartz crystal tuning fork resonator, capable ofvibrating in a fundamental mode, and having a high frequency stabilitywhich gives a high time accuracy.

It is a further object of the present invention to provide an electronicapparatus comprising a quartz crystal oscillator with alength-extensional mode quartz crystal resonator.

According to one aspect of the present invention, there is provided anelectronic apparatus comprising a display portion and a quartz crystaloscillator at least, and said electronic apparatus having one quartzcrystal oscillator, said one quartz crystal oscillator comprising: aquartz crystal oscillating circuit comprising; an amplification circuitcomprising an amplifier at least and a feedback circuit comprising aquartz crystal resonator and capacitors at least, said quartz crystalresonator being a quartz crystal tuning fork resonator, capable ofvibrating in a flexural mode, and said quartz crystal tuning forkresonator comprising: tuning fork tines each of which has a length, awidth and a thickness and the length greater than the width and thethickness; and a tuning fork base; said tuning fork tines and saidtuning fork base that are formed integrally; and electrodes disposedfacing each other on sides of said tuning fork tines so that theelectrodes disposed facing each other are of opposite electricalpolarity and said tuning fork tines are capable of vibrating in inversephase,

According to a second aspect of the present invention there is providedan electronic apparatus comprising a display portion and a quartzcrystal oscillator at least, and said electronic apparatus comprises atleast one quartz crystal oscillator comprising: an oscillating circuitcomprising; an amplification circuit comprising an amplifier at least,and a feedback circuit comprising a length-extensional mode quartzcrystal resonator which is one of a contour mode quartz crystalresonator.

According to a third aspect of the present invention, there is provideda method for manufacturing an electronic apparatus comprising a displayportion and a quartz crystal oscillator at least, and said electronicapparatus comprising at least one quartz crystal oscillator, said atleast one oscillator comprising: a quartz crystal oscillating circuitcomprising; an amplification circuit comprising an amplifier at least,and a feedback circuit comprising a quartz crystal resonator andcapacitors at least, said quartz crystal resonator being a quartzcrystal tuning fork resonator, capable of vibrating in a flexural mode,said quartz crystal tuning fork resonator comprising the steps of:forming integrally tuning fork tines each of which has a length, a widthand a thickness and the length greater than the width and the thicknessand a tuning fork base; disposing electrodes facing each other on sidesof said tuning fork tines so that the electrodes disposed facing eachother are of opposite electrical polarity and said tuning fork tinesvibrate an in inverse phase; and adjusting resonance frequency of saidquartz crystal tuning fork resonator after mounting it at a mountingportion by conductive adhesives or solder so that a frequency deviationis within a range of −100 PPM to +100 PPM.

According to a fourth aspect of the present invention, there areprovided a quartz crystal resonator, a quartz crystal unit and a quartzcrystal oscillator, each of which has a piezoelectric constant e₁₂ thatis within a range of 0.095 C/m² to 0.19 C/m².

Preferably, said tuning fork resonator is constructed so that figure ofmerit M₁ of a fundamental mode vibration is larger than figure of meritM₂ of a second overtone mode vibration.

Preferably, the quartz crystal oscillator with said tuning forkresonator is constructed so that a ratio of an amplification rate α₁ ofthe fundamental mode vibration and an amplification rate α₂ of thesecond overtone mode vibration of said amplification circuit is largerthan that of a feedback rate β₂ of the second overtone mode vibrationand a feedback rate β₁ of the fundamental mode vibration of saidfeedback circuit, and a product of the amplification rate α₁ and thefeedback rate β₁ of the fundamental mode vibration is larger than 1.

Preferably, the quartz crystal oscillator with said tuning forkresonator is constructed so that a ratio of an absolute value ofnegative resistance, |−RL₁| of the fundamental mode vibration of saidamplification circuit and series resistance R₁ of the fundamental modevibration is larger than that of an absolute value of negativeresistance, |−RL₂| of the second overtone mode vibration of saidamplification circuit and series resistance R₂ of the second overtonemode vibration.

Preferably, the length-extensional mode quartz crystal resonatorcomprises a vibrational portion, connecting portions and supportingportions, which are formed integrally by a particle method.

The present invention will be more fully understood by referring to thefollowing detailed specification and claims taken in connection with theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an embodiment of an electronic apparatusof the present invention, and illustrating the diagram of a facsimileapparatus;

FIG. 2 shows a diagram of an embodiment of a quartz crystal oscillatingcircuit constructing a quartz crystal oscillator, which constructs anelectronic apparatus of the present invention;

FIG. 3 shows a diagram of the feedback circuit of FIG. 2;

FIG. 4 shows a general view of a flexural mode, quartz crystal tuningfork resonator constructing a quartz crystal oscillator, whichconstructs an electronic apparatus of the first embodiment of thepresent invention;

FIG. 5 shows a A-A′ cross-sectional view of the tuning fork base of FIG.4, and illustrating electrode construction;

FIG. 6 shows a plan view of a quartz crystal tuning fork resonator ofFIG. 4;

FIG. 7 shows a plan view of a flexural mode, quartz crystal tuning forkresonator constructing a quartz crystal oscillator, which constructs anelectronic apparatus of the second embodiment of the present invention;

FIG. 8 a and FIG. 8 b show a top view and a side view of alength-extensional mode quartz crystal resonator constructing a quartzcrystal oscillator, which constructs an electronic apparatus of thethird embodiment of the present invention;

FIG. 9 shows a cross-sectional view of a quartz crystal unitconstructing a quartz crystal oscillator, which constructs an electronicapparatus of the fourth embodiment of the present invention;

FIG. 10 shows a cross-sectional view of a quartz crystal oscillator,which constructs an electronic apparatus of the fifth embodiment of thepresent invention;

FIG. 11 shows a step diagram of a method for manufacturing a quartzcrystal unit constructing a quartz crystal oscillator, which constructsan electronic apparatus of the present invention;

FIG. 12 is a general view of the conventional flexural mode, quartzcrystal tuning fork resonator constructing a quartz crystal oscillatorof the prior art, which constructs the conventional electronicapparatus;

FIG. 13 is a cross-sectional view of the tuning fork tines of FIG. 12,and illustrating electrode construction;

FIG. 14 shows a B-B′ cross-sectional view of the tuning fork tines ofFIG. 4;

FIG. 15 shows a plan view of a quartz crystal unit of the presentinvention and omitting a lid, and constructing a quartz crystaloscillator and an electronic apparatus of the present invention;

FIG. 16 shows a plan view of a quartz crystal unit of the presentinvention and omitting a lid, and constructing a quartz crystaloscillator and an electronic apparatus of the present invention;

FIG. 17 shows a plan view of a quartz crystal unit of the presentinvention and omitting a lid, and constructing a quartz crystaloscillator and an electronic apparatus of the present invention;

FIG. 18 shows a relationship between a dimensional ratio R=W₀/L₀ and acut angle θ_(x) of a length extensional mode quartz crystal resonator togive a zero temperature coefficient;

FIG. 19 shows a top view (a) and a C-C′ cross-sectional view (b) of avibrational portion of a thickness shear mode quartz crystal resonatorconstructing a quartz crystal unit, and which constructs an electronicapparatus of the present invention.

FIG. 20 shows a plan view of a flexural mode, quartz crystal tuning forkresonator of the present invention, and constructing a quartz crystalunit, a quartz crystal oscillator and an electronic apparatus of thepresent invention;

FIG. 21 shows a D₁-D₂ cross-sectional view of the tuning fork tines ofFIG. 20;

FIG. 22 shows a D₃-D₄ cross-sectional view of the tuning fork tines ofFIG. 20;

FIG. 23 shows a plan view of a flexural mode, quartz crystal tuning forkresonator of the present invention, and constructing a quartz crystalunit, a quartz crystal oscillator and an electronic apparatus of thepresent invention;

FIG. 24 shows a J₁-J₂ cross-sectional view of the tuning fork tines ofFIG. 23;

FIG. 25 shows a J₃-J₄ cross-sectional view of the tuning fork tines ofFIG. 23;

FIG. 26 shows a plan view of a flexural mode resonator of an embodimentof the present invention to construct a unit, an oscillator and anelectronic apparatus of the present invention;

FIG. 27 shows a Me-Me′ cross-sectional view of the flexural moderesonator of FIG. 26;

FIG. 28 shows a plan view of a flexural mode resonator of anotherembodiment of the present invention to construct a unit, an oscillatorand an electronic apparatus of the present invention;

FIG. 29 shows a Ms-Ms′ cross-sectional view of the flexural moderesonator of FIG. 28;

FIG. 30 shows a block diagram comprising a plurality of circuits of afirst embodiment of the present invention to get an output signal, andcomprising a phase locked loop circuit;

FIG. 31 shows a block diagram comprising a plurality of circuits of asecond embodiment of the present invention to get two output signals;and

FIG. 32 shows a block diagram comprising a plurality of circuits of athird embodiment of the present invention to get three output signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, the embodiments of the present inventionwill be described in more detail.

FIG. 1 shows a block diagram of an embodiment of an electronic apparatusof the present invention, and illustrating the diagram of a facsimileapparatus. As is shown in FIG. 1, the apparatus generally comprises amodem, a phonetic circuit, a timepiece circuit, a printing portion, ataking portion, an operation portion and a display portion. In thisprinciple, perception and scanning of reflection light of lightprojected on manuscript in the taking portion are performed byCCD(Charge Coupled Device), in addition, light and shade of thereflection light are transformed into a digital signal, and the signalis modulated by the modem and is sent to a phone line(Communicationline). Also, in a receiving side, a received signal is demodulated bythe modem and is printed on a paper in the print portion bysynchronizing the received signal with a signal of a sending side. Inaddition, the display portion comprises at least one of a liquid crystaldisplay (LCD) portion, a plasma display panel (PDP) portion, asurface-conduction electron-emitter display (SED) portion and an organicelectroluminescence display (OED) portion.

As shown in FIG. 1, a resonator, for example, a quartz crystal resonatorwhich is one of piezoelectric resonators made of piezoelectric materialsis used as a CPU clock of the control portion and the printing portion,as a clock of the phonetic circuit and the modem, and as a time standardof the timepiece. Namely, the quartz crystal resonator is used toconstruct a quartz crystal oscillator comprising a quartz crystaloscillating circuit having the quartz crystal resonator and an outputsignal of the quartz crystal oscillator is used. For example, it is usedas a signal, namely, as a clock signal to display time at the displayportion. In this case, to get the signal a resonator capable ofvibrating in a flexural mode, e.g. a quartz crystal tuning forkresonator, capable of vibrating in a flexural mode is used, and e.g. asthe CPU clock, a contour mode quartz crystal resonator such as alength-extensional mode quartz crystal resonator or a thickness shearmode quartz crystal resonator is used. In order to get the facsimileapparatus of this embodiment which operates normally, an accuracy outputsignal of the oscillator is required for the facsimile apparatus, whichis one of the electronic apparatus of the present invention. Also, adigital display and an analogue display are included in the display ofthe present invention. In this embodiment, two quartz crystal resonatorseach of which vibrates in a different mode are used in the electronicapparatus of the present invention. But, the present invention is notlimited to this, two quartz crystal resonators each of which vibrates inthe same mode may be used in the electronic apparatus of the presentinvention. In other words, each of two resonators vibrates in athickness shear mode or in a flexural mode, for example, when each ofthe two resonators is made of quartz crystal, each of the two quartzcrystal resonators vibrates in a thickness shear mode or in a flexuralmode. Namely, one of the two quartz crystal resonators is used as asignal for use in operation of the electronic apparatus to display timeinformation at the display portion of the electronic apparatus. One ofthe two quartz crystal resonators used as the signal for use inoperation of the electronic apparatus to display time information at thedisplay portion has a frequency of oscillation of a fundamental mode ofvibration. In more detail, a resonator has a fundamental mode ofvibration and an overtone mode of vibration. It is needless to say thatthe fundamental mode of vibration and the overtone mode of vibrationthereof are defined as the same mode of vibration. For example, when athickness shear mode quartz crystal resonator has a fundamental mode ofvibration and a third overtone mode of vibration, the fundamental modeof vibration of the thickness shear mode quartz crystal resonator is thesame mode of vibration as the third overtone mode of vibration thereof.In stead of the quartz crystal, such a piezoelectric material may beused as LiTaO₃, LiNbO₃, GaPO₄, and so on. Namely, though the quartzcrystal is used as a material of the resonators in this embodiment, itis needless to say that the resonators of this invention may be made ofany material. Therefore, a resonator capable of vibrating in a flexuralmode, made of a material may be used as at least one of the CPU clockand the time standard of the timepiece of the facsimile apparatus inthis embodiment. As is shown in FIG. 1, a plurality of resonatorscomprising first, second, third, fourth and fifth resonators each ofwhich is used to construct an oscillator having an oscillating circuit,are used for the facsimile in this embodiment of the electronicapparatus of the present invention. In addition, if need arises, anoscillation frequency of an output signal output from the oscillatingcircuit through a buffer circuit changes to at least one desiredoscillation frequency by using a divider (a dividing circuit) or byusing a PLL (Phase Locked Loop) circuit, and the at least one desiredoscillation frequency is used as a signal, namely, as a clock signal foruse in operation of the electronic apparatus of the present invention.For example, the signal is used to operate the CPU of the electronicapparatus or the signal is used to display time information at thedisplay portion of the electronic apparatus. In addition, the at leastone desired oscillation frequency comprises a plurality of differentoscillation frequencies to get a small-sized oscillator of a low cost,e.g. three different oscillation frequencies, one of which comprises afirst oscillation frequency of a first output signal output from theoscillating circuit through the buffer circuit, the first oscillationfrequency is the same as the oscillation frequency of the oscillatingcircuit, one of which comprises a second oscillation frequency of asecond output signal output from the oscillating circuit through thebuffer circuit and the dividing circuit, and one of which comprises athird oscillation frequency of a third output signal output from theoscillating circuit through the buffer circuit and the PLL circuit.

In this embodiment, though the facsimile apparatus is shown as anexample of an electronic apparatus, the present invention is not limitedto this, namely, the present invention includes all electronicapparatus, each of which comprises an oscillator, e.g. a quartz crystaloscillator and a display portion at least, for example, cellar phones,telephones, a TV set, cameras, a video set, video cameras, pagers,personal computers, printers, CD players, MD players, electronic musicalinstruments, car navigators, car electronics, timepieces, IC cards andso forth. In other words, this invention includes electronic apparatusescomprising two of the cellar phones, the telephones, the TV set, thecameras, the video set, the video cameras, the pagers, the personalcomputers, the printers, the CD players, the MD players, the electronicmusical instruments, the car navigators, the car electronics, thetimepieces, the IC cards and so forth, and the two is connectedelectrically each other. For example, one of the personal computer, thecamera and the video camera is electrically connected to the printer,and an output signal of the corresponding one of the personal computer,the camera and the video camera is a clock signal for use in operationof the printer. In addition, the electronic apparatus of the presentinvention may comprise a battery (cell), e.g. a lithium battery or afuel cell which is housed in the electronic apparatus of the presentinvention. In particular, the fuel cell may be used to charge a batteryhoused in the electronic apparatus of the present invention through aconnecting terminal.

FIG. 2 shows a diagram of an embodiment of a quartz crystal oscillatingcircuit constructing a quartz crystal oscillator, which constructs anelectronic apparatus of the present invention. The quartz crystaloscillating circuit 1 comprises an amplifier (CMOS Inverter) 2, afeedback resistor 4, a drain resistor 7, capacitors 5, 6 and a flexuralmode, quartz crystal tuning fork resonator 3. Namely, the oscillatingcircuit 1 comprises an amplification circuit 8 having the amplifier 2and the feedback resistor 4, and a feedback circuit 9 having the drainresistor 7, the capacitors 5, 6 and the quartz crystal tuning forkresonator 3. In addition, an output signal of the oscillating circuit 1comprising the quartz crystal tuning fork resonator 3, capable ofvibrating in a fundamental mode, is outputted through a buffer circuit(not shown in FIG. 2).

In detail, an oscillation frequency of the fundamental mode vibration isoutputted through a buffer circuit as an output signal. According to thepresent invention, a nominal frequency of the fundamental mode vibrationof the resonator is within a range of 10 kHz to 200 kHz. Especially,32.768 kHz is an important frequency. In general, the output signal hasan oscillation frequency which is within a range of −100 PPM to +100 PPMto the nominal frequency, e.g. 32.768 kHz. In more detail, the quartzcrystal oscillator in this embodiment comprises a quartz crystaloscillating circuit and a buffer circuit, namely, the quartz crystaloscillating circuit comprises an amplification circuit and a feedbackcircuit, and the amplification circuit comprises an amplifier and afeedback resistor, and the feedback circuit comprises a flexural mode,quartz crystal tuning fork resonator, a drain resistor and capacitors.Also, flexural mode, quartz crystal tuning fork resonators which areused in a quartz crystal oscillator will be described in FIG. 4-FIG. 7in detail. Instead of the flexural mode, quartz crystal tuning forkresonator, a contour mode resonator such as a length-extensional modequartz crystal resonator, a width-extensional mode quartz crystalresonator and a Lame mode quartz crystal resonator or a thickness shearmode quartz crystal resonator or a flexural mode resonator capable ofvibrating in a flexural mode may be used.

FIG. 3 shows a diagram of the feedback circuit of FIG. 2. Now, whenangular frequency ω_(i) of the flexural mode, quartz crystal tuning forkresonator 3, capable of vibrating in a flexural mode, a resistance R_(d)of the drain resistor 7, capacitance C_(g), C_(d) of the capacitors 5,6, crystal impedance R_(ei) of the quartz crystal resonator 3, an inputvoltage V₁, and an output voltage V₂ are taken, a feedback rate β_(i) isdefined by β_(i)=|V₂|_(i)/|V₁|_(i), where i shows vibration order, forexample, when i=1 and 2, they are for a fundamental mode vibration and asecond overtone mode vibration.

In addition, load capacitance C_(L) is given by C_(L)=C_(g)C_(d)/(C_(g)+C_(d)), and when C_(g)=C_(d)=C_(gd) and Rd>>R_(ei), thefeedback rate β_(i) is given by β_(i)=1/(1+kC_(L) ²), where k isexpressed by a function of ω_(i), R_(d) and R_(ei). Also, R_(ei) isapproximately equal to series resistance R_(i).

Thus, it is easily understood from a relationship of the feedback rateβ_(i) and load capacitance C_(L) that the feedback rate of resonancefrequency for a fundamental mode vibration and an overtone modevibration becomes large, respectively, according to decrease of loadcapacitance C_(L). Therefore, when C_(L) has a small value, anoscillation of the overtone mode occurs very easily, instead of that ofthe fundamental mode. This is the reason why the maximum amplitude ofthe overtone mode vibration becomes smaller than that of the fundamentalmode vibration, and the oscillation of the overtone mode satisfies anamplitude condition and a phase condition simultaneously which are thecontinuous condition of an oscillation in an oscillating circuit.

As it is also one object of the present invention to provide a quartzcrystal oscillator having a flexural mode, quartz crystal tuning forkresonator, capable of vibrating in a fundamental mode and having a highfrequency stability (high time accuracy) of an output signal, and havingreduced electric current consumption, in this embodiment, loadcapacitance C_(L) is less than 25 pF to reduce electric currentconsumption. To get much reduced electric current consumption, C_(L) ispreferably less than 15 pF because electric current consumption isproportional to C_(L).

In addition, in order to suppress a second overtone mode vibration andto obtain a quartz crystal oscillator having an output signal of anoscillation frequency of a fundamental mode vibration, the quartzcrystal oscillator in this embodiment is constructed so that itsatisfies a relationship of α₁/α₂>β₂/β₁ and α₁β₁>1, where α₁ and α₂ are,respectively, an amplification rate of the fundamental mode vibrationand the second overtone mode vibration of an amplification circuit, andβ₁ and β₂ are, respectively, a feedback rate of the fundamental modevibration and the second overtone mode vibration of a feedback circuit.

In other words, the quartz crystal oscillator is constructed so that aratio of the amplification rate α₁ of the fundamental mode vibration andthe amplification rate α₂ of the second overtone mode vibration of theamplification circuit is larger than that of the feedback rate β₂ of thesecond overtone mode vibration and the feedback rate β₁ of thefundamental mode vibration of the feedback circuit, and also a productof the amplification rate α₁ and the feedback rate β₁ of the fundamentalmode vibration is larger than 1. A description of the high frequencystability will be performed later.

Also, characteristics of the amplifier of the amplification circuitconstructing the quartz crystal oscillating circuit of this embodimentcan be expressed by negative resistance −RL_(i). For example, when i=1,negative resistance −RL₁ is for a fundamental mode vibration and wheni=2, negative resistance −RL₂ is for a second overtone mode vibration.In this embodiment, the quartz crystal oscillating circuit isconstructed so that a ratio of an absolute value of negative resistance,|−RL₁| of the fundamental mode vibration of the amplification circuitand series resistance R₁ of the fundamental mode vibration is largerthan that of an absolute value of negative resistance, |−RL₂| of thesecond overtone mode vibration of the amplification circuit and seriesresistance R₂ of the second overtone mode vibration. That is to say, theoscillating circuit is constructed so that it satisfies a relationshipof |−RL₁|/R₁>|−RL₂|/R₂. By constructing the oscillating circuit likethis, an oscillation of the second overtone mode can be suppressed, as aresult of which an output signal of a frequency of the fundamental modevibration can be provided because an oscillation of the fundamental modegenerates easily in the oscillating circuit.

FIG. 4 shows a general view of a flexural mode, quartz crystal tuningfork resonator 10 which is one of a contour mode resonator, constructinga quartz crystal oscillator, which constructs an electronic apparatus ofthe first embodiment of the present invention and its coordinate systemo-xyz. A cut angle θ which has a typical value of 0° to 10° is rotatedfrom a Z-plate perpendicular to the z axis about the x axis. Namely, theflexural mode, quartz crystal tuning fork resonator has the cut angle ofZYw(0° to 10°) according to an expression of the IEEE notation. Theresonator 10 comprises two tuning fork tines (vibrating tines) 20 and 26and a tuning fork base (a base) 40. The tines 20 and 26 have grooves 21and 27 respectively, with the grooves 21 and 27 extending into the base40. Also, the base 40 has the additional grooves 32 and 36. In addition,the tines 20 and 26 vibrate in a flexural mode of a fundamental mode andan inverse phase. As is shown in FIG. 4, each of the grooves 21 and 27has a first stepped portion and a second stepped portion opposite thefirst stepped portion in the width direction, and a third steppedportion connecting the first stepped portion to the second steppedportion.

FIG. 5 shows an A-A′ cross-sectional view of the tuning fork base 40 ofthe quartz crystal resonator 10 in FIG. 4. In FIG. 5, the shape of theelectrode construction within the base 40 for the quartz crystalresonator of FIG. 4 is described in detail. The section of the base 40which couples to the tine 20 has the grooves 21 and 22 cut into theobverse and reverse faces of the base 40. Also, the section of the base40 which couples to the tine 26 has the grooves 27 and 28 cut into theobverse and reverse faces of the base 40. In addition to these grooves,the base 40 has the grooves 32 and 36 cut between the grooves 21 and 27,and also, the base 40 has the grooves 33 and 37 cut between the grooves22 and 28. Similar to the grooves 21, 27, it is needless to say thateach of the grooves 22, 28 also has a first stepped portion and a secondstepped portion opposite the first stepped portion in the widthdirection, and a third stepped portion connecting the first steppedportion to the second stepped portion.

Furthermore, the grooves 21 and 22 have the first electrodes 23 and 24both of the same electrical polarity, the grooves 32 and 33 have thesecond electrodes 34 and 35 both of the same electrical polarity, thegrooves 36 and 37 have the third electrodes 38 and 39 both of the sameelectrical polarity, the grooves 27 and 28 have the fourth electrodes 29and 30 both of same electrical polarity and the sides of the base 40have the fifth and sixth electrodes 25 and 31, each of oppositeelectrical polarity. In more detail, the fifth, fourth, and secondelectrodes 25, 29, 30, 34 and 35 have the same electrical polarity,while the first, sixth and third electrodes 23, 24, 31, 38 and 39 havethe opposite electrical polarity to the others. Two electrode terminalsE and E′ are constructed. That is, the electrodes disposed inside thegrooves constructed opposite each other in the thickness (z axis)direction have the same electrical polarity. Also, the electrodesdisposed opposite each other across adjoining grooves have oppositeelectrical polarity.

In addition, the resonator has a thickness t of the tines or the tinesand the base, and a groove thickness to. It is needless to say that theelectrodes are disposed inside the grooves and on the sides of thetines. In this embodiment, the first electrodes 23 and 24 are disposedat the tine and the base, and also, the fourth electrodes 29 and 30 aredisposed at the tine and the base. In addition, the electrodes aredisposed on the sides of the tines opposite each other to the electrodesdisposed inside the grooves. Namely, the electrodes are disposedopposite each other inside the grooves and on the sides of the tines sothat the electrodes disposed opposite each other are of oppositeelectrical polarity. Additionally, electrodes are disposed facing eachother on the sides of the tines so that the electrodes disposed facingeach other are of opposite electrical polarity, and the tines arecapable of vibrating in inverse phase. In more detail, a first tuningfork tine and a second tuning fork tine, and a tuning fork base areformed integrally, an electrode is disposed on both sides of the firsttine and the second tine so that the electrodes disposed (facing eachother) on inner sides of the first and second tines are of oppositeelectrical polarity. Therefore, the disposition of the electrodesdisposed inside the grooves and on the sides of the tuning fork tines,described above is the same as that of the electrodes shown in FIG. 14which shows a B-B′ cross-sectional view of the tuning fork tines 20, 26of the quartz crystal resonator 10 in FIG. 4, namely, the electrodes 23,24 are connected to the electrodes 31, 43 to define an electrodeterminal F, while the electrodes 29, 30 are connected to the electrodes25, 44 to define an electrode terminal F′. It is needless to say thatthe electrode terminal F is electrically connected to the electrodeterminal E and the electrode terminal F′ is electrically connected tothe electrode terminal E′.

When a direct current voltage is applied between the electrode terminalsE and E′ (E terminal: plus, E′ terminal: minus), an electric field E_(x)occurs in the arrow direction as shown in FIG. 5. As the electric fieldE_(x) occurs perpendicular to the electrodes disposed on the base, theelectric field E_(x) has a very large value and a large distortionoccurs at the base, so that the quartz crystal tuning fork resonator isobtained with a small series resistance R₁ and a high quality factor Q₁,even if it is miniaturized.

FIG. 6 shows a plan view of the resonator 10 of FIG. 4. In FIG. 6, theconstruction and the dimension of grooves 21, 27, 32 and 36 aredescribed in detail. The groove 21 is constructed to include a portionof the central line 41 of the tine 20, and the groove 27 is similarlyconstructed to include a portion of the central line 42 of the tine 26.The width W₂ of the grooves 21 and 27 (groove width W₂) which include aportion of the central lines 41 and 42 respectively, is preferablebecause moment of inertia of the tines 20 and 26 becomes large and thetines can vibrate in a flexural mode easily. As a result, the quartzcrystal tuning fork resonator capable of vibrating in a fundamental modecan be obtained with a small series resistance R₁ and a high qualityfactor Q₁.

In more detail, when part widths W₁, W₃ and a groove width W₂ are taken,the tine width W of the tines 20 and 26 has a relationship ofW=W₁+W₂+W₃, and the part widths W₁, W₃ are constructed so that W₁≧W₃ orW₁<W₃. In addition, the groove width W₂ is constructed so that W₂≧W₁,W₃. In this embodiment, also, the grooves are constructed at the tinesso that a ratio (W₂/W) of the groove width W₂ and the tine width W islarger than 0.35 and less than 1, preferably larger than 0.35 and lessthan 0.85, and a ratio (t₁/t) of the groove thickness t₁ and thethickness t of the tines (tine thickness t) is less than 0.79,preferably, larger than 0.05 and less than 0.79, more preferably, largerthan 0.1 and less than 0.6 to obtain very large moment of inertia of thetines and a small motional inductance L₁ of the fundamental mode ofvibration. In more detail, when each of the grooves 21 and 27 formed inthe obverse faces of the tines 20 and 26 has a depth t₁ and each of thegrooves 22 and 28 formed in the reverse faces of the tines 20 and 26 hasa depth t₂, the thickness t is given by t=t₁+t₂+t₃, and t₁ and t₂ arelarger than 0.021 mm, preferably, larger than 0.025 mm and less than0.075 mm, more preferably, larger than 0.03 mm and less than 0.055 mm.That is, the flexural mode, quartz crystal tuning fork resonator,capable of vibrating in the fundamental mode, and having a goodfrequency stability can be provided with a small series resistance R₁, ahigh quality factor Q₁ and a small capacitance ratio r₁ becauseelectromechanical transformation efficiency of the resonator becomeslarge markedly.

Likewise, a length l₁ of the grooves 21, 27 provided at the tines 20, 26extends into the base 40 in this embodiment (which has a dimension ofthe length l₂ and the length l₃ of the grooves). Therefore, a groovelength and a length of the tines are given by (l₁-l₃) and (l-l₂),respectively, and a ratio of (l₁-l₃) and (l-l₂) is within a range of 0.3to 0.8, preferably, 0.4 to 0.8 to get a flexural mode tuning forkresonator with series resistance R₁ of a fundamental mode vibrationsmaller than series resistance R₂ of a second overtone mode vibration.In other words, a groove length is within a range of 30% to 80%,preferably, 40% to 80% of a length of each of the tines, so that aflexural mode tuning fork resonator with a reduced series resistance R₁and a small motional inductance L₁ of a fundamental mode vibration andhaving shock proof can be obtained when the flexural mode tuning forkresonator is miniaturized. Also, a length l₂ of the base is less than0.5 mm, preferably, within a range of 0.29 mm to 0.48 mm or within arange of 0.12 mm to 0.255 mm or within a range of 0.264 mm to 0.277 mm,so that a miniaturized flexural mode tuning fork resonator can beobtained with reduced energy losses which are caused by vibration whenit is mounted on a mounting portion of a case. As be well known, theresonator can be expressed by an electrical equivalent circuitcomprising motional capacitance C₁, motional inductance L₁, seriesresistance R₁ connected in series, and shunt capacitance C₀ connected toC₁, L₁ and R₁ in parallel.

Furthermore, the total length l is determined by the frequencyrequirement and the size of the housing case. Simultaneously, to get aflexural mode, quartz crystal tuning fork resonator, capable ofvibrating in a fundamental mode with suppression of the second overtonemode vibration which is an unwanted mode vibration, there is a closerelationship between the groove length l₁ and the total length l.Namely, a ratio (l₁/l) of the groove length l₁ and the total length l iswithin a range of 0.2 to 0.78 because the quantity of charges whichgenerate within the grooves and on the sides of the tines or the tinesand the base can be controlled by the ratio, as a result, the secondovertone mode vibration which is an unwanted mode vibration, can besuppressed, and simultaneously, a frequency stability of the fundamentalmode vibration gets high. Therefore, the flexural mode, quartz crystaltuning fork resonator, capable of vibrating easily in a fundamental modeand having high frequency stability can be provided. Also, the totallength l is less than 2.18 mm, preferably, within a range of 1.2 mm to 2mm, more preferably, 0.8 mm to 1.2 mm, and groove length l₁ is less than1.29 mm, preferably, within a range of 0.32 mm to 1.1 mm, morepreferably, within a range of 0.32 mm to 0.85 mm, to get a smaller-sizedtuning fork resonator with about 32.768 kHz and a small motionalinductance L₁ which vibrates in a flexural mode and a fundamental mode.

In more detail, series resistance R₁ of the fundamental mode vibrationbecomes smaller than series resistance R₂ of the second overtone modevibration. Namely, R₁<R₂, preferably, R₁<0.86R₂, therefore, a quartzcrystal oscillator comprising an amplifier (CMOS inverter), capacitors,resistors and a quartz crystal unit with the quartz crystal tuning forkresonator of this embodiment can be obtained, which is capable ofvibrating in the fundamental mode easily. In addition, in thisembodiment the grooves 21 and 27 of the tines 20 and 26 extend into thebase 40 in series, but embodiment of the present invention includes aplurality of grooves divided into the length direction of the tines. Inaddition, the grooves may be constructed only at the tines (l₃=0). Fromthe relationship of l₃=0, each of the grooves 21, 22, 27 and 28 has afirst stepped portion and a second stepped portion opposite the firststepped portion in the width direction, and a third stepped portion anda fourth stepped portion opposite the third stepped portion in thelength direction.

In this embodiment, the groove length l corresponds to electrode lengthdisposed inside the grooves, though the electrode is not shown in FIG.6, but, when the electrode length is less than the groove length, thelength l₁ is of the electrode length. Namely, the ratio (l₁/l) in thiscase is expressed by a ratio of electrode length l of the grooves andthe total length l. In order to achieve the above-mentioned object, itmay be satisfied with at least one groove with the ratio constructed atthe obverse and reverse faces of each tine. As a result, the flexuralmode, quartz crystal tuning fork resonator, capable of vibrating veryeasily in the fundamental mode and having the high frequency stabilitycan be realized. Also, a fork portion of this embodiment has arectangular shape, but this invention is not limited to this, forexample, the fork portion may have a U shape.

In addition, a spaced-apart distance between the tines is given by W₄,and in this embodiment, the space W₄ and the groove width W₂ areconstructed so that W₄≧W₂, and more, the space W₄ is within a range of0.05 mm to 0.35 mm and the groove width W₂ is within a range of 0.03 mmto 0.12 mm because it is easy to form a tuning fork shape and grooves ofthe tuning fork tines separately by a photo-lithographic process and anetching process, consequently, a frequency stability for a fundamentalmode vibration gets higher than that for a second overtone modevibration. In this embodiment, a quartz wafer with the thickness t of0.05 mm to 0.18 mm is used. In order to get a smaller-sized quartzcrystal tuning fork resonator, capable of vibrating in a flexural mode,and a small motional inductance L₁, it is necessary that groove width W₂is less than 0.07 mm, preferably, larger than 0.015 mm and less than0.04 mm and tine width W is less than 0.18 mm, and preferably, the W islarger than 0.05 mm and less than 0.1 mm, more preferably, larger than0.03 mm and less than 0.075 mm. Also, a groove thickness t₁ is within arange of 0.01 mm to 0.085 mm approximately, and part widths W₁, W₃ areless than 0.021 mm, preferably, less than 0.015 mm. In more detail, adimension of the part widths W₁, W₃ is very dependent on a manufacturingtechnology. Therefore, when the technology is taken into account, W₁ andW₃ have a value of larger than 0.004 mm, preferably, larger than 0.008mm and less than 0.015 mm, more preferably, larger than 0.01 mm and lessthan 0.014 mm to get a small motional inductance L₁. In addition, thegroove provided on at least one of the obverse face and the reverse faceof the tuning fork tines of the present invention may be a through hole,namely, the groove thickness t₁=0. Moreover, another example of thetuning fork tines having t₁=0 is shown in FIG. 20 and which shows a planview of a flexural mode, quartz crystal tuning fork resonator 600. Indetail, the resonator 600 comprises tuning fork tines 601, 602 andtuning fork base 603, the base 603 has cut portions 604, 605, and thetines 601, 602 have central linear portions 616, 617, respectively. Thetine 601 has through holes 606, 608, 610 and grooves 607, 609 and thetine 602 has through holes 611, 613, 615 and grooves 612, 614. Each ofthe tines 601, 602 has a width W, and the through holes and the grooveshave a width W₂ larger than or equal to part widths W₁, W₃, where W isgiven by W=W₁+W₂+W₃. Namely, the tuning fork tines have a first tuningfork tine 601 and a second tuning fork tine 602, and three through holesare formed at each of the first and second tuning fork tines so that awidth W₂ of the through holes is greater than the part widths W₁ and/orW₃. For example, the width W₂ of the through holes has a value lagerthan 0.02 mm and less than 0.04 mm and the part widths W₁ and W₃ have avalue larger than 0.008 mm and less than 0.014 mm. In this embodiment,the through holes are dived into the length direction of the first andsecond tuning fork tines. When the first tuning fork tine 601 has threethrough holes comprising first, second and third through holes 610, 608,606 divided in the length direction, the groove 609 is formed betweenthe first through 610 and second through hole 608 and the groove 606 isformed between the second through hole 608 and the third through hole606. Similar to this, when the second tuning fork tine 602 has threethrough holes comprising first, second and third through holes 615, 613,611 divided in the length direction, the groove 614 is formed betweenthe first through 615 and second through hole 613 and the groove 612 isformed between the second through hole 613 and the third through hole611. In other words, each of the first and second tuning fork tines hasthree through holes divided in the length direction and a groove isformed in at least one or each of the obverse and reverse faces betweentwo through holes. In this embodiment, though a groove is formed betweentwo through holes, but this invention is not limited to this, the groovemay be not formed between the two through holes. Namely, a frame portionis formed between the two through holes. In addition, FIG. 21 shows aD₁-D₂ cross-sectional view of the tuning fork tines 601, 602. The tine601 has electrodes 618, 621 disposed on side surfaces and electrodes619, 620 disposed in grooves 609, 626, while the tine 602 has electrodes622, 625 disposed on side surfaces and electrodes 623, 624 disposed ingrooves 614, 627. The electrodes 618, 621, 623, 624 are connectedelectrically to form an electrode terminal G₁, while the electrodes 619,620, 622, 625 are connected electrically to form an electrode terminalG₂. Moreover, FIG. 22 shows a D₃-D₄ cross-sectional view of the tuningfork tines 601, 602. The tine 601 has electrodes 618, 621 disposed onside surfaces and electrodes 628, 629 disposed in a through hole 610,while the tine 602 has electrodes 622, 625 disposed on side surfaces andelectrodes 630, 631 disposed in a through hole 615. The electrodes 618,621, 630, 631 are connected electrically to form an electrode terminalG₃, while the electrodes 628, 629, 622, 625 are connected electricallyto form an electrode terminal G₄. The electrode terminals G₁ and G₃ havethe same electrical polarity, while the electrode terminals G₂ and G₄have the same electrical polarity different from the electrical polarityof the electrode terminals G₁ and G₃. When an alternating currentvoltage is applied to the electrode terminals G₁, G₃ and the electrodeterminals G₂, G₄, the tuning fork resonator vibrates in a flexural modeof an inverse phase. In this embodiment, frame portions are not shown atthe tuning fork base 603, but the tuning fork base may have frameportions protruding from the tuning fork base. Moreover, when a lengthof the grooves and a length of the through holes are defined by l_(m)and l_(a), respectively, there are two relationships so that l_(m)≧l_(a)or l_(m)<l_(a). In more detail, a length l_(a) of the through holes inthis embodiment is within a range of 0.03 mm to 0.45 mm, preferably,0.05 mm to 0.3 mm and a length l_(m) of the grooves is within a range of0.01 mm to 0.5 mm, preferably, 0.025 mm to 0.35 mm. One of the tworelationships is selected so that the tuning fork resonator has a smallmotional inductance L₁. It is needless to say that a relationship of thelength l_(a) and the length l_(m) can be applied to a tuning forkresonator in FIG. 23. In addition, a further example of the tuning forktines having t₁=0 is shown in FIG. 23 and which shows a plan view of aflexural mode, quartz crystal tuning fork resonator 650. In detail, theresonator 650 comprises tuning fork tines 651, 652 and tuning fork base653, the base 653 has cut portions 654, 655, and the tines 651, 652 havecentral linear portions 666, 667, respectively. The tine 651 has throughholes 656, 657, 658, 659 and a groove 660 and the tine 652 has throughholes 661, 662, 663, 664 and a groove 665. Each of the tines 601, 602has a width W, and the grooves have a width W₂ larger than or equal topart widths W₁, W₃, where W is given by W=W₁+W₂+W₃. Namely, when each ofthe first and second tuning fork tines has a first side surface and asecond side surface opposite the first side surface, and obverse andreverse faces each of which has a central linear portion, a through holeis formed between the first side surface and the central linear portionand/or a through hole is formed between the second side surface and thecentral linear portion so that the central linear portion is notincluded in the through hole. Namely, a width of the through hole isless than a half of the tine width W. In this embodiment, the throughholes are divided into the width and length directions of thecorresponding one of the first and second tuning fork tines. The groove660 is formed between the through holes 656, 657, between the throughholes 658, 659, between 656, 658 and between the through holes 657, 659,while the groove 665 is formed between the through holes 661, 662,between the through holes 663, 664, between 661, 663 and between thethrough holes 662, 664. Namely, the through holes 656, 657, 658, 659 areformed in the groove 660 and the through holes 661, 662, 663, 664 areformed in the groove 665. In this embodiment, though a groove is formedbetween the through holes, this invention is not limited to this, butthe groove may be not formed between the through holes. In addition, twothrough holes at each of left and right sides of the central linearportion are formed in the length direction in this embodiment, but thethrough holes more than two may be formed in the length direction. Inaddition, two through holes are formed symmetrically in the widthdirection to the central linear portion in this embodiment, but the twothrough holes may be formed asymmetrically in the width direction to thecentral linear portion. Moreover, FIG. 24 shows a J₁-J₂ cross-sectionalview of the tuning fork tines 651, 652. The tine 651 has electrodes 668,672 disposed on side surfaces and electrodes 669, 670, 671 disposed inthrough holes 656, 657, while the tine 652 has electrodes 673, 678disposed on side surfaces and electrodes 674, 675, 676 disposed inthrough hole 661, 662. The electrodes 668, 672, 674, 675, 676 areconnected electrically to form an electrode terminal N₁, while theelectrodes 669, 670, 671, 673, 678 are connected electrically to form anelectrode terminal N₂. In addition, FIG. 25 shows a J₃-J₄cross-sectional view of the tuning fork tines 651, 652. The tine 651 haselectrodes 668, 672 disposed on side surfaces and electrodes 679, 680disposed in grooves 660, 683, while the tine 652 has electrodes 673, 678disposed on side surfaces and electrodes 681, 682 disposed in grooves665, 684. The electrodes 668, 672, 681, 682 are connected electricallyto form an electrode terminal N₃, while the electrodes 679, 680, 673,678 are connected electrically to form an electrode terminal N₄. Theelectrode terminals N₁ and N₃ have the same electrical polarity, whilethe electrode terminals N₂ and N₄ have the same electrical polaritydifferent from the electrical polarity of the electrode terminals N₁ andN₃. When an alternating current voltage is applied to the electrodeterminals N₁, N₃ and the electrode terminals N₂, N₄, the tuning forkresonator vibrates in a flexural mode of an inverse phase. In thisembodiment, frame portions are not shown at the tuning fork base 653,but the tuning fork base may have frame portions protruding from thetuning fork base. Moreover, the through holes are formed at each offirst and second tuning fork tines by etching simultaneously with thefirst and second tuning fork tines. But, at least one through hole maybe formed at each of first and second tuning fork tines by etching in astep different from the step of forming the first and second tuning forktines. In addition, each of the first and second tuning fork tines has aplurality of through holes in the length direction, an overall length ofthe through holes is within a range of 20% to 80%, preferably, 30% to70%, of a length of each of the tuning fork tines. Moreover, when awidth of the groove formed in the width direction between two throughholes and a width of the through holes are defined by w_(m) and w_(a),respectively, the groove and the through holes are formed so thatw_(m)≧w_(a) or w_(m)<w_(a). Namely, they are formed so that the tuningfork resonator has a small motional inductance L₁. Also, a width of thethrough holes in this embodiment is within a range of 0.008 mm to 0.03mm, preferably, 0.01 mm to 0.02 mm. As a result, the tuning forkresonator can be obtained with a small motional inductance L₁, so thatan oscillating circuit with the tuning fork resonator can be providedwith short rise-time of an output signal when an alternating currentvoltage is applied to the oscillating circuit. In addition, an anotherexample of metal films disposed on opposite main surfaces and oppositeside surface of each of tuning fork tines of a tuning fork resonator ofthe present invention is shown in detail. That is to say, the tuningfork resonator comprises a tuning fork base and the tuning fork tinesconnected to the tuning fork base. In detail, the tuning fork tines havea first tuning fork tine and a second tuning fork tine each of which hasa first vibrational portion having a thickness t₁₁ connected to thetuning fork base, a second vibrational portion having a thickness t₂₂less or greater than or equal to the thickness t₁₁ connected to thefirst vibrational portion and a third vibrational portion having athickness t₃₃ less or greater than or equal to the thickness t₂₂connected to the second vibrational portion in the length direction (notshown here), for example, t₂₂ is equal to t₁₁ and less than t₃₃ or t₂₂is less than t₁₁ and equal to t₃₃ or t₂₂ is less than t₁₁ and t₃₃ isgreater than t₁₁ or t₂₂ is greater than t₁₁ and equal to t₃₃ or t₂₂ isgreater than t₁₁ and t₃₃ is greater than t₂₂. In particular, when thethickness t₂₂ is the same as the thickness t₁₁ so that t₂₂ is equal tot₁₁ and less than t₃₃, the first vibrational portion (thickness t₁₁) andthe second vibrational portion (thickness t₂₂) are newly replaced with afirst vibrational portion having a thickness t₁₂=t₁₁=t₂₂ and the thirdvibrational portion is newly replaced with a second vibrational portionhaving a thickness t₁₃=t₃₃. Similar to this, when the thickness t₂₂ isthe same as the thickness t₃₃ so that t₂₂ is equal to t₃₃ and greaterthan t₁₁, the second vibrational portion (thickness t₂₂) and the thirdvibrational portion (thickness t₃₃) are newly replaced with a secondvibrational portion having a thickness t₂₃=t₂₂=t₃₃. As above-described,each of the tuning fork tines comprises a plurality of differentthicknesses, e.g. having a first thickness and a second thicknessgreater than the first thickness. In more detail, each of the first,second and third vibrational portions has a first end portion and asecond end portion opposite the first end portion in the lengthdirection. Also, the first vibrational portion has a first main surfaceand a second main surface opposite the first main surface, the secondvibrational portion has a third main surface and a fourth main surfaceopposite the third main surface and the third vibrational portion has afifth main surface and a sixth main surface opposite the fifth mainsurface. The first end portion of the first vibrational portion isconnected to the tuning fork base and the second end portion of thefirst vibrational portion is connected to the first end portion of thesecond vibrational portion. In addition, the second end portion of thesecond vibrational portion is connected to the first end portion of thethird vibrational portion and the second end portion of the thirdvibrational portion is free in vibration. Similar to this, the firstvibrational portion has a first side surface and a second side surfaceopposite the first side surface, the second vibrational portion has athird side surface and a fourth side surface opposite the third sidesurface and the third vibrational portion has a fifth side surface and asixth side surface opposite the fifth side surface. Namely, the secondvibrational portion is located between the first and third vibrationalportions. In addition, at least one metal film (at least one electrode)is disposed on each of the first and second main surfaces and the firstand second side surfaces of the first vibrational portion of each of thefirst and second tuning fork tines. In detail, the at least one metalfilm comprises a first metal film, e.g. the first metal film compriseschromium, and an insulation material on the chromium or the at least onemetal film comprises a plurality of metal films having a first metalfilm and a second metal film, e.g. the first metal film compriseschromium and the second metal film comprises gold formed on thechromium, and an insulation material formed on the gold. Also, the atleast one metal film disposed on each of the first and second mainsurfaces of the first vibrational portion of the first tuning fork tineis electrically connected to the at least one metal film disposed oneach of the first and second side surfaces of the first vibrationalportion of the second tuning fork tine to define a first electrodeterminal and the at least one metal film disposed on each of the firstand second side surfaces of the first vibrational portion of the firsttuning fork tine is electrically connected to the at least one metalfilm disposed on each of the first and second main surfaces of the firstvibrational portion of the second tuning fork tine to define a secondelectrode terminal. In order to get the tuning fork resonator with adecreased series resistance R₁ and a small motional inductance L₁, agroove is formed in each of the first and second main surfaces of thefirst vibrational portion of each of the first and second tuning forktines. In this case, the metal films disposed on the first and secondmain surfaces of the first vibrational portion are, therefore, disposedon surfaces of the grooves formed in the first and second main surfacesof the first vibrational portion. Namely, the at least one metal film isdisposed on each of the first and second main surfaces of the firstvibrational portion of each of the first and second tuning fork tinesand each of the surfaces of the grooves formed in the first and secondmain surfaces of the first vibrational portion of each of the first andsecond tuning fork tines. In addition, at least two metal films aredisposed on at least one of the third and fourth main surfaces of thesecond vibrational portion of each of the first and second tuning forktines. In detail, the at least two metal films comprise a first metalfilm and a second metal film formed on the first metal film, e.g. thefirst metal film comprises chromium and the second metal film comprisesgold (thickness t_(g1)) or the first metal film comprises chromium andthe second metal film comprises silver (thickness t_(s1)). Also, athickness of the first metal film is less or greater than that of thesecond metal film. Namely, two kinds of metal films made of differentmaterials, respectively, are disposed on at least one of the third andfourth main surfaces of the second vibrational portion of each of thefirst and second tuning fork tines. Similar to this, a plurality ofmetal films are disposed on at least one of the fifth and sixth mainsurfaces of the third vibrational portion of each of the first andsecond tuning fork tines. In detail, the plurality of metal filmscomprise a first metal film and a second metal film formed on the firstmetal film, e.g. the first metal film comprises chromium and the secondmetal film comprises gold (thickness t_(g2)) or the first metal filmcomprises chromium and the second metal film comprises silver (thicknesst_(s2)). In this embodiment, the thickness t_(g2) of the gold or thethickness t_(s2) of the silver is greater than the thickness of thesecond metal film disposed on the at least one of the third and fourthmain surfaces of the second vibrational portion of each of the first andsecond tuning fork tines. In addition, as an another example, theplurality of metal films disposed on at least one of the fifth and sixthmain surfaces of the third vibrational portion of each of the first andsecond tuning fork tines comprise a first metal film, a second metalfilm formed on the first metal film and a third metal film formed on thesecond metal film and the third metal film is formed in a step differentfrom the step of forming the second metal film, e.g. the first metalfilm comprises chromium, the second metal film comprises gold (thicknesst_(g3)) and the third metal film comprises gold (thickness t_(g4)) whichis formed through a mask in a step different from the step of formingthe second metal film with the thickness t_(g3) of the gold or the firstmetal film comprises chromium, the second metal film comprises gold(thickness t_(g3)) and the third metal film comprises silver (thicknesst_(s3)). In more detail, a thickness of the second metal film is lessthan that of the third metal film, the thickness t_(g3) of the gold ofthe second metal film is substantially equal to the thickness of thesecond metal film disposed on the at least one of the third and fourthmain surfaces of the second vibrational portion of each of the first andsecond tuning fork tines, and the thickness t_(g3) of the gold of thesecond metal film is greater or less than the thickness t_(g4) of thegold of the third metal film or the thickness t_(s3) of the silver ofthe third metal film. Likewise, the thickness of the first metal filmdisposed on each of the first and second main surfaces of the firstvibrational portion of each of the first and second tuning fork tines isless than the thickness of the third metal film disposed on the at leastone of the fifth and sixth main surfaces of the third vibrationalportion of each of the first and second tuning fork tines. Also, amaterial of the first metal film disposed on each of the first andsecond main surfaces and the first and second side surfaces of the firstvibrational portion of each of the first and second tuning fork tines isthe same as that of the first metal film disposed on the at least one ofthe third and fourth main surfaces of the second vibrational portion ofeach of the first and second tuning fork tines and/or the first metalfilm disposed on the at least one of the fifth and sixth main surfacesof the third vibrational portion of each of the first and second tuningfork tines, e.g. the material comprises chromium or tin or nickel oraluminium. Moreover, a thickness of the first metal film disposed oneach of the first and second main surfaces and/or the first and secondside surfaces of the first vibrational portion of each of the first andsecond tuning fork tines is substantially equal to that of the firstmetal film disposed on the at least one of the third and fourth mainsurfaces of the second vibrational portion of each of the first andsecond tuning fork tines and/or the first metal film disposed on the atleast one of the fifth and sixth main surfaces of the third vibrationalportion of each of the first and second tuning fork tines. In order toget an enough binding force which occurs between each of the mainsurfaces and the first metal film comprising the chromium or the tin orthe nickel or the aluminium disposed on each of the main surfaces, thethickness of the first metal film is in the range of 350 A to 1500 A,where A represents a unit of angstrom. Next, an embodiment of a methodfor manufacturing the tuning fork resonator with the tuning fork baseand the first and second tuning fork tines each having the metal filmsabove-described is shown in detail. According to the present invention,after a tuning fork shape comprising the tuning fork base and the firstand second tuning fork tines connected to the tuning fork base areformed by etching a quartz crystal wafer, the metal films disposed onthe main surfaces of each of the first and second tuning fork tines areformed by a plurality of steps. Namely, the plurality of steps comprisethe steps of forming the first metal film and the second metal film onthe first metal film on each of the first and second main surfaces andeach of the first and second side surfaces of each of the first andsecond tuning fork tines, forming the first and second metal films on atleast one of the third and fourth main surfaces of each of the first andsecond tuning fork tines and forming the first, second and third metalfilms on at least one of the fifth and sixth main surfaces of each ofthe first and second tuning fork tines. In more detail, the method formanufacturing the tuning fork resonator in this embodiment comprises theplurality of steps of A.) forming the first metal film on each of thefirst, second, third, fourth, fifth and sixth main surfaces and thefirst, second, third, fourth, fifth and sixth side surfaces of each ofthe first and second tuning fork tines, B.) forming the second metalfilm on the first metal film on each of the first, second, third,fourth, fifth and sixth main surfaces and the first, second, third,fourth, fifth and sixth side surfaces of each of the first and secondtuning fork tines, C.) forming a resist on the second metal film formedon the first metal film, D.) electrically connecting the first metalfilm or the second metal film on the first metal film disposed on eachof the first and second main surfaces of the first vibrational portionof the first tuning fork tine to the first metal film or the secondmetal film on the first metal film disposed on each of the first andsecond side surfaces of the first vibrational portion of the secondtuning fork tine to define a first electrode terminal and electricallyconnecting the first metal film or the second metal film on the firstmetal film disposed on each of the first and second side surfaces of thefirst vibrational portion of the first tuning fork tine to the firstmetal film or the second metal film on the first metal film disposed oneach of the first and second main surfaces of the first vibrationalportion of the second tuning fork tine to define a second electrodeterminal, E.) forming the third metal film through a mask on at leastone of the fifth and sixth main surfaces of each of the first and secondtuning fork tines by an evaporation method or a sputtering method, F.)adjusting an oscillation frequency of the tuning fork resonator bytrimming the third metal film disposed on the at least one of the fifthand sixth main surfaces of the third vibrational portion of each of thefirst and second tuning fork tines, and G.) eliminating the second metalfilm formed on the first metal film on each of the first and second mainsurfaces and the first and second side surfaces of the first vibrationalportion of each of the first and second tuning fork tines by a chemicaletching method. In this embodiment, e.g. the first metal film comprisesa chromium film or a tin film or a nickel film or an aluminium film or atitanium film or a tungsten film, the second metal film comprises a goldfilm or a silver film or an aluminium film or a copper film or a tinfilm or a titanium film or a tungsten film and the third metal filmcomprises a gold film or a silver film. Also, the first, second andthird metal films are formed by a sputtering method or an evaporationmethod, respectively. According to the present invention, e.g. theplurality of steps are performed in the order of A.), B.), C.), D.),E.), and F.). Also, the step of G.) is performed after the step of C.)or D.). In addition, a method for manufacturing the tuning forkresonator with the first and second tuning fork tines in an anotherembodiment of the present invention comprises the plurality of steps ofA.) forming the first metal film on each of the first, second, third,fourth, fifth and sixth main surfaces and the first, second, third,fourth, fifth and sixth side surfaces of each of the first and secondtuning fork tines, B.) forming the second metal film on the first metalfilm on each of the first, second, third, fourth, fifth and sixth mainsurfaces and the first, second, third, fourth, fifth and sixth sidesurfaces of each of the first and second tuning fork tines, C.) forminga resist on the second metal film formed on the first metal film, D.)eliminating the second metal film formed on the first metal film formedon each of the first and second main surfaces of the first vibrationalportion of each of the first and second tuning fork tines and the firstmetal film formed on each of the first and second main surfaces of thefirst vibrational portion of each of the first and second tuning forktines by a chemical etching method so that two electrical insulationportions are formed on each of the first and second main surfaces of thefirst vibrational portion of each of the first and second tuning forktines, each of the two insulation portions has a width Wi in the rangeof 0.005 mm to 0.045 mm, preferably, 0.015 mm to 0.035 mm and a lengthLi in the range of 0.5 mm to 1.7 mm, and the first metal film and thesecond metal film on the first metal film disposed on each of the firstand second main surfaces of the first vibrational portion of the firsttuning fork tine are electrically connected to the first metal film andthe second metal film on the first metal film disposed on each of thefirst and second side surfaces of the first vibrational portion of thesecond tuning fork tine to define a first electrode terminal and thefirst metal film and the second metal film on the first metal filmdisposed on each of the first and second side surfaces of the firstvibrational portion of the first tuning fork tine are electricallyconnected to the first metal film and the second metal film on the firstmetal film disposed on each of the first and second main surfaces of thefirst vibrational portion of the second tuning fork tine to define asecond electrode terminal, E.) forming the third metal film through amask on at least one of the fifth and sixth main surfaces of each of thefirst and second tuning fork tines, and F.) adjusting an oscillationfrequency of the tuning fork resonator by trimming the third metal filmdisposed on the at least one of the fifth and sixth main surfaces of thethird vibrational portion of each of the first and second tuning forktines. Preferably, the plurality of steps in this embodiment areperformed in the order of A.), B.), C.), D.), E.), and F.). In addition,a method for manufacturing the tuning fork resonator in a furtherembodiment of the present invention comprises the plurality of steps ofA.) forming the first metal film on each of the first, second, third,fourth, fifth and sixth main surfaces and the first, second, third,fourth, fifth and sixth side surfaces of each of the first and secondtuning fork tines, B.) forming the second metal film on the first metalfilm on each of the first, second, third, fourth, fifth and sixth mainsurfaces and the first, second, third, fourth, fifth and sixth sidesurfaces of each of the first and second tuning fork tines, C.) forminga resist on the second metal film formed on the first metal film, D.)eliminating the second metal film formed on the first metal film formedon each of the first and second main surfaces of the first vibrationalportion of each of the first and second tuning fork tines and the firstmetal film formed on each of the first and second main surfaces of thefirst portion of each of the first and second tuning fork tines by achemical etching method so that two electrical insulation portions areformed on each of the first and second main surfaces of the firstvibrational portion of each of the first and second tuning fork tines,each of the two insulation portions having a width Wi in the range of0.005 mm to 0.045 mm, preferably, 0.015 mm to 0.035 mm and a length Liin the range of 0.5 mm to 1.7 mm, and eliminating the second metal filmformed on the first metal film disposed on each of the first and secondmain surfaces and the first and second side surfaces of the firstvibrational portion of each of the first and second tuning fork tines sothat the first metal film disposed on each of the first and second mainsurfaces of the first vibrational portion of the first tuning fork tineis electrically connected to the first metal film disposed on each ofthe first and second side surfaces of the first vibrational portion ofthe second tuning fork tine to define a first electrode terminal and thefirst metal film disposed on each of the first and second side surfacesof the first vibrational portion of the first tuning fork tine iselectrically connected to the first metal film disposed on each of thefirst and second main surfaces of the first vibrational portion of thesecond tuning fork tine to define a second electrode terminal, E.)forming the third metal film through a mask on at least one of the fifthand sixth main surfaces of each of the first and second tuning forktines, and F.) adjusting an oscillation frequency of the tuning forkresonator by trimming the third metal film disposed on the at least oneof the fifth and sixth main surfaces of the third vibrational portion ofeach of the first and second tuning fork tines. Preferably, theplurality of steps in this embodiment are performed in the order of A.),B.), C.), D.), E.), and F.). Also, insulation materials are formed onthe first and second main surfaces of the first and second tuning forktines after the step of D.) to prevent short-circuit which generatesbetween the first and second electrode terminals, and at least one ofthe insulation materials comprises S_(i)O₂. In the embodimentsabove-described, the tuning fork resonator is shown with the first andsecond tuning fork tines. But, it is needless to say that the presentinvention includes a flexural mode resonator with a vibrational arminstead of the tuning fork resonator comprising the first and secondtuning fork tines. In addition, a method for manufacturing the tuningfork resonator in a still further embodiment of the present inventioncomprises the plurality of steps of A.) forming the first metal film oneach of the first, second, third, fourth, fifth and sixth main surfacesand the first, second, third, fourth, fifth and sixth side surfaces ofeach of the first and second tuning fork tines, B.) forming the secondmetal film on the first metal film on at least one of the third andfourth main surfaces and at least one of the fifth and sixth mainsurfaces of each of the first and second tuning fork tines, C.) forminga resist on the second metal film on the first metal film on at leastone of the third and fourth main surfaces and at least one of the fifthand sixth main surfaces of each of the first and second tuning forktines and the first metal film on each of the first and second mainsurfaces and the first and second side surfaces of each of the first andsecond tuning fork tines, D.) eliminating the first metal film formed oneach of the first and second main surfaces of the first vibrationalportion of each of the first and second tuning fork tines by a chemicaletching method so that two electrical insulation portions are formed oneach of the first and second main surfaces of the first vibrationalportion of each of the first and second tuning fork tines and the firstmetal film disposed on each of the first and second main surfaces of thefirst vibrational portion of the first tuning fork tine is electricallyconnected to the first metal film disposed on each of the first andsecond side surfaces of the first vibrational portion of the secondtuning fork tine to define a first electrode terminal and the firstmetal film disposed on each of the first and second side surfaces of thefirst vibrational portion of the first tuning fork tine is electricallyconnected to the first metal film disposed on each of the first andsecond main surfaces of the first vibrational portion of the secondtuning fork tine to define a second electrode terminal, E.) forming thethird metal film through a mask on at least one of the fifth and sixthmain surfaces of each of the first and second tuning fork tines, and F.)adjusting an oscillation frequency of the tuning fork resonator bytrimming the third metal film disposed on the at least one of the fifthand sixth main surfaces of the third vibrational portion of each of thefirst and second tuning fork tines. In general, the plurality of stepsin this embodiment are performed in the order of A.), B.), C.), D.),E.), and F.). In addition, the third main surface comprises the firstmain surface and the fifth main surface comprises the third mainsurface, and the fourth main surface comprises the second main surfaceand the sixth main surface comprises the fourth main surface, namely,each of the third and fifth main surfaces comprises the first mainsurface and each of the fourth and sixth main surfaces comprises thesecond main surface. With respect to the side surfaces, the relationshipof the side surfaces can be obtained by replacing “main” with “side”.

In more detail, to obtain a flexural mode, quartz crystal tuning forkresonator with a high frequency stability which gives high timeaccuracy, it is necessary to obtain the resonator whose resonancefrequency is not influenced by shunt capacitance because quartz crystalis a piezoelectric material and the frequency stability is verydependent on the shunt capacitance. In order to decrease the influenceon the resonance frequency by the shunt capacitance, figure of meritM_(i) (hereafter a merit value M_(i)) plays an important role. Namely,the merit value M_(i) that expresses inductive characteristics,electromechanical transformation efficiency and a quality factor of aflexural mode, quartz crystal tuning fork resonator, is defined by aratio (Q_(i)/r_(i)) of a quality factor Q_(i) and capacitance ratior_(i), namely, M_(i) is given by M_(i)=Q_(i)/r_(i), where i showsvibration order of the resonator, and for example, when i=1 and 2, themerit values M₁ and M₂ are a value for a fundamental mode vibration anda second overtone mode vibration of the flexural mode, quartz crystaltuning fork resonator, respectively.

Also, a frequency difference Δf of resonance frequency f_(s) ofmechanical series independent on the shunt capacitance and resonancefrequency f_(r) dependent on the shunt capacitance is inverselyproportional to the merit value M_(i). The larger the value M_(i)becomes, the smaller the difference Δf becomes. Namely, the influence onthe resonance frequency f_(r) by the shunt capacitance decreases becauseit is close to the resonance frequency f_(s). Accordingly, the largerthe M_(i) becomes, the higher the frequency stability of the flexuralmode, quartz crystal tuning fork resonator becomes because the resonancefrequency f_(r) of the resonator is almost never dependent on the shuntcapacitance. Namely, the quartz crystal tuning fork resonator can beprovided with a high time accuracy.

In detail, the flexural mode, quartz crystal tuning fork resonator canbe obtained with the merit value M₁ of the fundamental mode vibrationlarger than the merit value M₂ of the second overtone mode vibration bythe above-described tuning fork shape, grooves and dimensions. That isto say, a relationship of M₁>M₂ is obtained. As an example, whenresonance frequency of a flexural mode, quartz crystal tuning forkresonator is about 32.768 kHz for a fundamental mode vibration and theresonator has a value of W₂/W=0.5, t₁/t=0.34 and l₁/l=0.48, though thereis a distribution in production, the resonator has a value of M₁>65 andM₂<30, respectively.

Namely, the flexural mode, quartz crystal tuning fork resonator whichvibrates in the fundamental mode can be provided with high inductivecharacteristics, good electromechanical transformation efficiency (smallcapacitance ratio r₁ and small series resistance R₁) and a high qualityfactor. As a result, a frequency stability of the fundamental modevibration becomes higher than that of the second overtone modevibration, and simultaneously, the second overtone mode vibration can besuppressed because capacitance ratio r₂ and series resistance R₂ of thesecond overtone mode vibration become larger than capacitance ratio r₁and series resistance R₁ of the fundamental mode vibration,respectively. In particular, r₂ has a value larger than 1500 in thisembodiment.

Therefore, the resonator capable of vibrating in the fundamental modevibration can be provided with a high time accuracy because it has thehigh frequency stability. Consequently, a quartz crystal oscillatorcomprising the flexural mode, quartz crystal tuning fork resonator ofthis embodiment outputs an oscillation frequency of the fundamental modevibration as an output signal, and the frequency of the output signalhas a very high stability, namely, excellent time accuracy. In otherwords, the quartz crystal oscillator of this embodiment has a remarkableeffect such that a frequency change by ageing becomes extremely small.Also, an oscillation frequency of the resonator of this embodiment isadjusted so that a frequency deviation is within a range of −100 PPM to+100 PPM to a nominal frequency, e.g. 32.768 kHz, after mounting it at amounting portion of a case or a lid by conductive adhesives or solder.

In addition, the groove thickness t₁ of the present invention is thethinnest thickness of the grooves because quartz crystal is ananisotropic material and the groove thickness t₁ has a distribution whenit is formed by a chemical etching method. In detail, a groove shape ofthe sectional view of tuning fork tines in FIG. 5 has a rectangularshape, but the groove shape has an about U shape or a complicated shapeactually because an etching speed of a plus x-axis direction of quartzcrystal in the chemical etching method is different from that of a minusx-axis direction thereof. It is, therefore, clear that the groove shapeof the sectional view of the tuning fork tines in FIG. 5 changes by acondition of concentration and temperature of etching liquids and bychemical etching processes to form the groove. It is needless to saythat the groove shape can be formed with the about U shape by optimizingthe condition of concentration and temperature of the etching liquidsand by devising the chemical etching processes. In the above-describedembodiments, though the grooves are constructed at the tines, thisinvention is not limited to this, namely, a relationship of the meritvalues M₁ and M₂ can be applied to the conventional flexural mode,quartz crystal tuning fork resonator and a relationship of a quartzcrystal oscillating circuit comprising an amplification circuit and afeedback circuit can be also applied to the conventional flexural mode,quartz crystal tuning fork resonator to suppress a second overtone modevibration and to get a high frequency stability for a fundamental modevibration of the tuning fork resonator.

FIG. 7 shows a plan view of a flexural mode, quartz crystal tuning forkresonator 45 which is one of a contour mode quartz crystal resonator,constructing a quartz crystal oscillator, which constructs an electronicapparatus of the second embodiment of the present invention. Theresonator 45 comprises tuning fork tines 46, 47 and a tuning fork base48. The tines 46, 47 and the base 48 are formed integrally by a chemicaletching process. In this embodiment, the base 48 has cut portions 53 and54. Also, a groove 49 is constructed to include a portion of the centralline 51 of the tine 46, and a groove 50 is similarly constructed toinclude a portion of the central line 52 of the tine 47. In thisembodiment, the grooves 49 and 50 are constructed at a part of the tines46 and 47, and have groove width W₂ and groove length l₁. In moredetail, a groove area S (=W₂×l₁) has a value of 0.01 mm² to 0.12 mm²,preferably, greater than 0.01 mm² and less than 0.043 mm² because it isvery easy to form the grooves by a chemical etching process and thequartz crystal tuning fork resonator can be provided with goodelectromechanical transformation efficiency by the formation of thegrooves.

Namely, the quartz crystal tuning fork resonator, capable of vibratingin a fundamental mode and having a high frequency stability can beprovided with a small series resistance R₁ and a high quality factor Q₁.Therefore, a quartz crystal oscillator having the high frequencystability can be realized with an output signal of a frequency of thefundamental mode vibration. In this embodiment, though electrodes arenot shown in FIG. 7, the electrodes are disposed inside the grooves 49,50 and on sides of the tines 46 and 47, similar to the resonator of FIG.4. In detail, the electrodes are disposed opposite each other inside thegrooves and on the sides of the tines so that the electrodes disposedopposite each other are of opposite electrical polarity. In more detail,a groove is provided on both of an obverse face and a reverse face oftuning fork tines having a first tuning fork tine and a second tuningfork tine, and also, a first electrode is disposed inside the groove anda second electrode is disposed on both sides of the tuning fork tines.In addition, a quartz crystal tuning fork resonator has two electrodeterminals, the one of the electrode terminals comprises a firstelectrode disposed inside a groove provided on both of the obverse faceand the reverse face of the first tuning fork tine and a secondelectrode disposed on the both sides of the second tuning fork tine,such that the first and second electrodes are connected, and the otherof the electrode terminals comprises a second electrode disposed on theboth sides of the first tuning fork tine and a first electrode disposedinside a groove provided on both of the obverse face and the reverseface of the second tuning fork tine, such that the second and firstelectrodes are connected. In this embodiment, a groove is provided onboth of an obverse face and a reverse face of tuning fork tines, but thepresent invention in not limited to this, for example, a groove may beprovided on at least one of an obverse face and a reverse face of tuningfork tines.

In addition, the base 48 has cut portions 53 and 54, and the cut base 48has a dimension of width W₅ (tines side) and width W₆ (opposite side tothe tines side). Also, the cut base 48 has a length l₄ between one ofthe cut portions and the side opposite to the tines side, and the lengthl₄ is greater than 0.03 mm and less than 0.48 mm, preferably, within arange of 0.05 mm to 0.3 mm, more preferably, 0.12 mm to 0.25 mm toreduce energy losses which are caused by vibration. In addition, when alength l₅ is defined by l₅=l₂−l₄, l₄ is less than or equal to l₅ toachieve the decreased energy losses. When the base 48 is mounted at amounting portion (e.g. on two lead wires for a package of a tubulartype) of a case or a lid of a surface mounting type or a tubular type bysolder or conductive adhesives, it is necessary to satisfy W₆≧W₅ todecrease energy losses by vibration. The cut portions 53 and 54 are veryeffective to decrease the energy losses. Therefore, the flexural mode,quartz crystal tuning fork resonator, capable of vibrating in thefundamental mode and having the high frequency stability (high timeaccuracy) can be provided with a small series resistance R₁ and a highquality factor Q₁. Also, the width dimensions W=W₁+W₂+W₃ and W₄, and thelength dimensions l₁, l₂ and l are as already described in relation toFIG. 6. In addition, a shape of the tuning fork base according to thepresent invention is not limited to that of this embodiment, forexample, a tuning fork base may have a frame portion protruding from thetuning fork base, and the frame portion is mounted at a mounting portionof a case or a lid of a package. The matter described above impliesthat, for example, when the tuning fork tines have a first tuning forktine and a second tuning fork tine, the first tuning fork tine isbetween the second tuning fork tine and the frame portion protrudingfrom the tuning fork base as shown in FIG. 15 which shows a plan view ofa quartz crystal unit and omitting a lid. In more detail, the quartzcrystal unit 250 comprises a quartz crystal tuning fork resonator 255capable of vibrating in a flexural mode of an inverse phase, a case 256for housing the resonator and a lid for covering an open end of the case(not shown here). Namely, the resonator 255 comprises tuning fork tines257, 258 and a tuning fork base 259 connected to the tuning fork tines,and the tuning fork base 259 has a frame portion 260 protruding from thetuning fork base. Also, the case 256 has mounting portions 261 and 262,and the frame portion 260 is mounted on the mounting portion 261 of thecase 256. In detail, an electrode 267 disposed at the frame portion 260is connected to an electrode 268 disposed on the mounting portion 261 byadhesives 263 or a metal such as solder, and similarly, an electrode 269disposed on the tuning fork base 259 is connected to an electrode 270disposed on the mounting portion 262 by adhesives 264 or a metal such assolder. In addition, the tuning fork tines 257, 258 have grooves 271,273 (not shown here), 272 and 274 (not shown here), the grooves 271 and272 are formed opposite to the grooves 273 and 274 in the thicknessdirection, respectively. The electrodes 271 a and 273 a disposed insidethe grooves 271 and 273 of the tine 257 are connected to the electrodes275 and 276 disposed on side surfaces of the tine 258 to define a firstelectrode terminal, while the electrodes 272 a and 274 a disposed insidethe grooves 272 and 274 of the tine 258 are connected to the electrodes277 and 278 disposed on side surfaces of the tine 257 to define a secondelectrode terminal. Moreover, each of the tines 257, 258 has a width Wwhich is a first width of a first vibrational portion and a width W_(g)which is a second width of a second vibrational portion, greater thanthe width W, preferably, the width W_(g) is less than three times of thewidth W to get a small motional inductance L₁. As a result of which thetuning fork resonator can be provided with a smaller size because thewidth W_(g) operates as mass and a short length of the tuning fork tinescan be obtained for a frequency of oscillation, e.g. 32.768 kHz. Forexample, when the width W is larger than 0.03 mm and less than 0.075 mm,the width W_(g) is larger than 0.04 mm and less than 0.23 mm. Forexample, a difference (W_(g)−W) is within a range of 0.008 mm to 0.1 mm,preferably, 0.01 mm to 0.05 mm to get enough mass effect. Also, each ofthe tines 257, 258 has a length l_(g) less than about 80% of a length ofeach of the tines measured from the free end of each of the tines. Thisis the reason why when each of the tines has the width W with afrequency, e.g. 32.8 kHz with the length l_(g)=0, about the samefrequency can be obtained as the frequency of 32.8 kHz for the width Wby forming the length l_(g) of about 80%. Namely, the tuning forkresonator can be obtained with a small motional inductance L₁ becausethe width of the tines becomes larger actually and the electromechanicaltransformation efficiency gets larger. In order to get a large masseffect by the length l_(g), each of the tines, preferably, has thelength l_(g) less than a half of the length of each of the tinesmeasured from the free end of each of the tines. For example, the lengthl_(g) is larger than 0.15 mm and less than 1.1 mm, preferably, largerthan 0.2 mm and less than 0.7 mm. In general, metal films for adjustingan oscillation frequency of the resonator are formed on main surfaceshaving the width W_(g), and the oscillation frequency is adjusted bytrimming at least one of the metal films. In addition, the tuning forkbase has cut portions 265, 266 and the length l₄, and the frame portionis connected to the tuning fork base having the length l₄. In addition,another example is shown in FIG. 16 which shows a plan view of a quartzcrystal unit and omitting a lid. In more detail, the quartz crystal unit350 comprises a quartz crystal tuning fork resonator 355 capable ofvibrating in a flexural mode of an inverse phase, a case 356 for housingthe resonator and a lid for covering an open end of the case (not shownhere). Namely, the resonator 355 comprises tuning fork tines 357, 358and a tuning fork base 359 connected to the tuning fork tines, and thetuning fork base 359 has two frame portions 360 a, 360 b protruding fromthe tuning fork base. Also, the case 356 has mounting portions 361 and362, and the frame portions 360 a and 360 b is, respectively, mounted onthe mounting portion 361 and 362 of the case 356. In detail, anelectrode 367 disposed at the frame portion 360 a is connected to anelectrode 368 disposed on the mounting portion 361 by adhesives 363 or ametal such as solder, and similarly, an electrode 369 disposed at theframe portion 360 b is connected to an electrode 370 disposed on themounting portion 362 by adhesives 364 or a metal such as solder. Inaddition, the tuning fork base has two cut portions 365 and 366, thetuning fork tines 357, 358 have the same as the grooves, the electrodesand the shape of the tuning fork tines shown in FIG. 15. When the quartzcrystal tuning fork resonator 355 in this embodiment is formed in aquartz crystal wafer, an end portion of the frame portion 360 a is notconnected to an end portion of the frame portion 360 b, as is shown inFIG. 16, but the present invention is not limited to this, namely, theend portion of the frame portion 360 a may be connected to the endportion of the frame portion 360 b to get a connected (closed) frameportion. In detail, the connected (closed) frame portion comprises oneend portion and the other end portion each connected to the tuning forkbase. Also, each of the connected frame portion and the tuning fork basehas an obverse face and a reverse face, namely, a first surface and asecond surface opposite the first surface. In this case, a quartzcrystal unit comprises a case and a lid, and each of the case and thelid has an interior space and an open end. Also, the reverse face (thesecond surface) of each of the connected frame portion and the tuningfork base is mounted on a mounting portion of the case and the obverseface (the first surface) of each of the connected frame portion and thetuning fork base is mounted on a mounting portion of the lid, namely,the reverse face (the second surface) of each of the connected frameportion and the tuning fork base is connected to the open end of thecase and the obverse face (the first surface) of each of the connectedframe portion and the tuning fork base is connected to the open end ofthe lid to cover the open end of each of the case and the lid. A widthof the open end of each of the lid and the case is less, preferably,equal to, more preferably, greater than a width of the connected frameportion or the tuning fork base to get a big connected power. When eachof the case and the lid has no through hole, at least one of the openend of the case and open end of the lid is connected to thecorresponding one of the obverse and reverse faces of each of theconnected frame portion and the tuning fork base so that the quartzcrystal tuning fork resonator is maintained in a vacuum, and when one ofthe case and the lid has a through hole including a first diameter and asecond diameter greater than the first diameter, a metal or a glass isdisposed into the through hole of the second diameter to close thethrough hole of one of the case and the lid in a vacuum after the openend of each of the case and the lid is connected to the correspondingone of the obverse and reverse faces of each of the connected frameportion and the tuning fork base. As above-described, the tuning forkbase is located between the open end of the case and the open end of thelid, for example, in FIG. 7, a part having an area of W₆xl₄ of thetuning fork base is located between the open end of the case and theopen end of the lid. It is needless to say that the quartz crystaltuning fork tines are located between the interior space of the case andthe interior space of the lid. Also, the connection of the open end ofthe case is performed simultaneously with the connection of the open endof the lid, but, according to the present invention, the connection ofthe open end of the case may be performed in a step different from theconnection of the open end of the lid, namely, the connection of theopen end of the case is performed after or before the connection of theopen end of the lid is performed. Also, a first electrode (metal film)is disposed on each of a surface of the open end of the lid and theobverse face of each of the connected frame portion and the tuning forkbase and a second electrode (metal film) is disposed on each of asurface of the open end of the case and the reverse face of each of theconnected frame portion and the tuning fork base. The lid is connectedto the connected frame portion and the tuning fork base through thefirst electrode disposed on the surface of the open end and the firstelectrode disposed on the obverse face, while the case is connected tothe connected frame portion and the tuning fork base through the secondelectrode disposed on the surface of the open end and the secondelectrode disposed on the reverse face. Namely, each of the connectionof the lid and the connected frame portion and the tuning fork base andthe connection of the case and the connected frame portion and thetuning fork base is performed by an anode connection method. Inaddition, the first electrode disposed on each of the surface of theopen end and the obverse face has an electrical polarity opposite to anelectrical polarity of the second electrode disposed on each of thesurface of the open end and the reverse face. Also, the case and the lidare made of a piezoelectric material such as quartz crystal or a glassor ceramics and have a thermal expansion coefficient less than that ofthe quartz crystal tuning fork resonator. In addition, a further exampleis shown in FIG. 17 which shows a plan view of a quartz crystal unit andomitting a lid. In more detail, the quartz crystal unit 450 comprises aquartz crystal tuning fork resonator 455 capable of vibrating in aflexural mode of an inverse phase, a case 456 for housing the resonatorand a lid for covering an open end of the case (not shown here). Namely,the resonator 455 comprises tuning fork tines 457, 458 and a tuning forkbase 459 connected to the tuning fork tines, and the tuning fork base459 has a frame portion 460 protruding from the tuning fork base. Also,the case 456 has mounting portions 461, and the frame portion 460 ismounted on the mounting portion 461 of the case 456. In detail, anelectrode 467 disposed at the frame portion 460 is connected to anelectrode 468 disposed on the mounting portion 461 by adhesives 463 or ametal such as solder, and similarly, an electrode 469 disposed at theframe portion 460 is connected to an electrode 470 disposed on themounting portion 461 by adhesives 464 or a metal such as solder. Inaddition, the tuning fork tines 457, 458 have the same as the groovesand the electrodes shown in FIG. 14. Namely, the frame portionprotruding from the tuning fork base is between the first tuning forktine and the second tuning fork tine, and is mounted on the mountingportion of the case. In addition, when each of the first and secondtuning fork tines has a mass M_(t) and the frame portion has a massM_(f), a summation of (2M_(t)+M_(f)) is greater than a mass M_(b) of thetuning fork base having a length l₂ to get good shock-proof, preferably,a summation of (2M_(t)+M_(f)/2) is greater than a mass M_(b) of thetuning fork base to get further good shock-proof. In addition, anexample of a flexural mode resonator 700 capable of vibrating in aflexural mode is shown in FIG. 26, and which shows a plan view of theflexural mode resonator 700 of an embodiment of the present invention toconstruct a unit, an oscillator and an electronic apparatus of thepresent invention. Namely, the unit comprises the flexural moderesonator housed in a case and a lid to cover an open end of the case.In detail, the flexural mode resonator is formed integrally with thecase (not shown here). Also, the oscillator comprises the unit and theelectronic apparatus comprises the oscillator. In detail, the resonator700 comprises vibrational arms 701, 702, connecting frames 703, 704,705, 706 and a frame 715. Each of the vibrational arms 701, 702 has alength L_(n) and a width W_(s) greater than a width W_(f) and a widthW_(t), in general, there is a relationship of W_(f)=W_(t). Also, one endportion of each of the vibrational arms 701, 702 is connected to theconnecting frame 703 and the other end portion of each of thevibrational arms 701, 702 is connected to the connecting frame 704.Namely, the resonator 700 comprises a boundary condition of“clamped-clamped”, so called a clamped-clamped type resonator andvibrates in a flexural mode, e.g. in the width direction in thisembodiment. By taking the width W_(s) greater than the width W_(f) andthe width W_(t), the resonator vibrates in a flexural mode with a highstability of frequency because it has the maximum amplitude in thevicinity of half a length (L_(n)/2) and has a large moment of inertia.In addition, each of the connecting frames 703, 704 is connected to theconnecting frames 705, 706, the connecting frames 705, 706 haveelectrodes 707, 710 and the frame 715 has electrodes 708, 709, while thevibrational arm 701 has electrodes 711, 712 and the vibrational arm 702has electrodes 713, 714. Also, though the width W_(s) is greater thanthe width W_(f) and the width W_(t) in this embodiment, the width W_(s)may be equal to the width W_(f) and the width W_(t), where W_(f)=W_(t).In addition, FIG. 27 shows a Me-Me′ cross-sectional view of the flexuralmode resonator of FIG. 26. Each of the vibrational arms 701, 702 has afirst side surface and a second side surface opposite the first sidesurface. The electrodes 711, 712 are disposed on the first and secondside surfaces of the vibrational arm 701 and the electrodes 713, 714 aredisposed on the first and second side surfaces of the vibrational arm702. The first side surface of the vibrational arm 701 is formedopposite to a side surface of the connecting frame 705 so that aspaced-apart distance between the first side surface and the sidesurface is less than 1.5 μm, preferably, in the range of 0.25 μm to 0.8μm, and the electrode 707 is disposed on the side surface of theconnecting frame 705, while the second side surface of the vibrationalarm 701 is formed opposite to a side surface of the frame 715 and theelectrode 708 is disposed on the side surface of the frame 715. Similarto this, the first side surface of the vibrational arm 702 is formedopposite to a side surface of the connecting frame 706 and the electrode710 is disposed on the side surface of the connecting frame 706, whilethe second side surface of the vibrational arm 702 is formed opposite toa side surface of the frame 715 and the electrode 709 is disposed on theside surface of the frame 715. The electrodes 711, 714 have the sameelectrical polarity to define a first electrode terminal A and theelectrodes 712, 713 have the same electrical polarity to define a secondelectrode terminal B. In addition, the electrodes 707, 708, 709, and 710have the same electrical polarity and are connected to an electrodeterminal of a bias voltage 716 (a plus voltage in this embodiment),where an electrode terminal of a minus voltage is connected to an earthelectrode (ground) C in this embodiment. Each of the electrodes 707,708, 709, 710 is disposed extending to an obverse face and a reverseface of each of the connecting frames 705, 706 and the frame 715 andeach of the electrodes 711, 712, 713, 714 is disposed extending to anobverse face and a reverse face of each of the vibrational arms 701,702. But, according to this invention, the electrodes 707, 708, 709, and710 may be connected to the electrode terminal of the bias voltagehaving either the plus voltage or the minus voltage. When an alternatingcurrent voltage is applied between the first electrode terminal A andthe second electrode terminal B, an electrostatic force, so called“Coulomb's force” occurs between the bias voltage and the electrodedisposed on each of the first and second side surfaces of thevibrational arms. As a result, each of the vibrational arms 701, 702vibrates in a flexural mode. Namely, the resonator 700 can vibrate in aflexural mode of an inverse phase in this embodiment. In order todecrease a shunt capacitance in an electrical equivalent circuit whichgenerates between the electrodes, a method for connecting the electrodesshown in FIG. 27 and the polarity of the electrodes may be changed. Inmore detail, the electrodes 711, 712, 713, and 714 are electricallyconnected to an electrode terminal of a bias voltage having either aplus voltage or a minus voltage, the electrodes 707 is electricallyconnected to the electrode 710 to define a first electrode terminal andthe electrodes 708 is electrically connected to the electrode 709 todefine a second electrode terminal. An alternating current voltage isapplied between the first and second electrode terminals to drive thevibrational arms in a flexural mode of an inverse phase in thisembodiment. As a result, the resonator can be achieved with a decreasedshunt capacitance. As is apparent from FIG. 27, when the electrode withthe bias voltage is disposed opposite to the electrode disposed on eachof the first and second side surfaces of each of the vibrational arms,an alternating current voltage is applied between the electrodesdisposed on the first and second side surfaces of each of thevibrational arms. On the contrary, when the electrode with the biasvoltage is disposed on each of the first and second side surfaces ofeach of the vibrational arms, an alternating current voltage is appliedbetween the electrode disposed opposite to each of the first sidesurfaces of the vibrational arms and the electrode disposed opposite toeach of the second side surfaces of the vibrational arms. In otherwords, when the electrode disposed opposite to the electrode of thefirst side surface of the vibrational arm and the electrode of the firstside surface of the vibrational arm are disposed so that an attractiveforce occurs between them, the electrode disposed opposite to theelectrode of the second side surface of the vibrational arm and theelectrode of the second side surface of the vibrational arm are disposedso that a repulsive force occurs between them, inversely, when theelectrode disposed opposite to the electrode of the first side surfaceof the vibrational arm and the electrode of the first side surface ofthe vibrational arm are disposed so that the repulsive force occursbetween them, the electrode disposed opposite to the electrode of thesecond side surface of the vibrational arm and the electrode of thesecond side surface of the vibrational arm are disposed so that theattractive force occurs between them. As a result, the vibrational armcan vibrate in a flexural mode. In the electrode disposition of thisembodiment shown in FIG. 26, the resonator can vibrate in a fundamentalmode of a flexural mode. In order that the resonator vibrates in anovertone mode easily, a plurality of electrodes are disposed on at leastone, preferably, each of the first and second side surfaces of thevibrational arms, e.g. when the resonator vibrates in a second overtonemode, two electrodes are disposed on at least one, preferably, each ofthe first and second side surfaces of the vibrational arms, and each ofthe two electrodes has an electrode opposite to each of the twoelectrodes. Similar to this, when the resonator vibrates in a thirdovertone mode, three electrodes are disposed on at least one,preferably, each of the first and second side surfaces of thevibrational arms, and each of the three electrodes has an electrodeopposite to each of the three electrodes. As is apparent from thisrelation, when the resonator vibrates in an n-order overtone mode,n-electrodes are disposed on at lest one, preferably, each of the firstand second side surfaces of the vibrational arms, and each of then-electrodes has an electrode opposite to each of the n-electrodes,where n has a value of 2, 3, 4, 5, 6, 7, etc. In detail, when theplurality of electrodes are disposed on at least one, preferably, eachof the first and second side surfaces of the vibrational arms, theelectrodes adjoining each other, disposed on the first and second sidesurfaces of the vibrational arms have a different electrical polarity.Namely, the plurality of electrodes and the electrode opposite to eachof the plurality of electrodes are disposed so that the attractive forceand the repulsive force occurs alternately to the vibrational arms todrive the n-order overtone mode. In this embodiment, though theplurality of electrodes are disposed on the first and second sidesurfaces of the vibrational arms, the plurality of electrodes aredisposed opposite to the electrode of each of the first and second sidesurfaces of the vibrational arms, when a bias voltage is applied to theelectrode of each of the first and second side surfaces of thevibrational arms. In addition, FIG. 28 shows a plan view of a flexuralmode resonator of another embodiment of the present invention toconstruct a unit, an oscillator and an electronic apparatus of thepresent invention. Namely, the unit comprises the flexural moderesonator housed in a case and a lid to cover an open end of the case.In detail, the flexural mode resonator is formed integrally with thecase (not shown here). Also, the oscillator comprises the unit and theelectronic apparatus comprises the oscillator. In detail, the resonator720 comprises a vibrational arm 721, a base portion 722 and connectingframes 723, 724. The vibrational arm 721 has a length L_(n) and a widthW_(s) greater than a width W_(f). Also, one end portion of thevibrational arm 721 is connected to the base portion 722 and the otherend portion is free in vibration. Namely, the resonator 720 comprises aboundary condition of “clamped-free”, so called a clamped-free typeresonator and vibrates in a flexural mode, e.g. in the width directionin this embodiment. The base portion 722 of the resonator 720 isconnected to the case in which the resonator is housed. Namely, theresonator comprising the vibrational arm, the base portion and theconnecting frames is formed integrally with the case. Likewise,according to the present invention, the vibrational arm may be directlyconnected to the case. By taking the width W_(s) greater than the widthW_(f), the resonator vibrates in a flexural mode with a high stabilityof frequency because it has the maximum amplitude at the free endportion and has a large moment of inertia. In addition, each of theconnecting frames 723, 724 is connected to the base portion 722, and theconnecting frames 723, 724 have electrodes 725, 726, while thevibrational arm 721 has electrodes 727, 728. Also, though the widthW_(s) is greater than the width W_(f) in this embodiment, the widthW_(s) may be equal to or less than the width W_(f) to get an enoughshock-proof. In addition, FIG. 29 shows a Ms-Ms′ cross-sectional view ofthe flexural mode resonator of FIG. 28. The vibrational arm 721 has afirst side surface and a second side surface opposite the first sidesurface. The electrode 727 is disposed on the first side surface of thevibrational arm 721 to define a first electrode terminal D and theelectrode 728 is disposed on the second side surface of the vibrationalarm 721 to define a second electrode terminal E. The first side surfaceof the vibrational arm 721 is formed opposite to a side surface of theconnecting frame 723 and the electrode 725 is disposed on the sidesurface of the connecting frame 723, while the second side surface ofthe vibrational arm 721 is formed opposite to a side surface of theconnecting frame 724 and the electrode 728 is disposed on the sidesurface of the connecting frame 724. Each of the electrodes 725, 726 isdisposed extending to an obverse face and a reverse face of each of theconnecting frames 723, 724 and each of the electrodes 727, 728 isdisposed extending to an obverse face and a reverse face of thevibrational arm 721. In addition, the electrodes 725, 726 have the sameelectrical polarity and are connected to an electrode terminal of a biasvoltage 729 (a plus voltage in this embodiment), where an electrodeterminal of a minus voltage is connected to an earth electrode (ground)F in this embodiment. But, according to this invention, the electrodes725, 726 may be connected to the electrode terminal of either the plusvoltage or the minus voltage. When an alternating current voltage isapplied between the first electrode terminal D and the second electrodeterminal E, an electrostatic force occurs between the bias voltage andthe electrode disposed on each of the first and second side surfaces ofthe vibrational arm. As a result of which the vibrational arm 721vibrates in a flexural mode. In order to decrease a shunt capacitance inan electrical equivalent circuit which generates between the electrodes,according to the present invention, a method for connecting theelectrodes shown in FIG. 29 and the polarity of the electrodes may bechanged. In more detail, the electrodes 727, 728 are electricallyconnected to an electrode terminal of a bias voltage of either a plusvoltage or a minus voltage, the electrode 725 is disposed on the sidesurface of the connecting frame 723 to define a first electrode terminaland the electrode 726 is disposed on the side surface of the connectingframe 724 to define a second electrode terminal. An alternating currentvoltage is applied between the first and second electrode terminals todrive the vibrational arm in a flexural mode. As a result of which theresonator can be achieved with a decreased shunt capacitance. As isapparent from FIG. 29, when the electrode with the bias voltage isdisposed opposite to the electrode disposed on each of the first andsecond side surfaces of the vibrational arm, an alternating currentvoltage is applied between the electrodes disposed on the first andsecond side surfaces of the vibrational arm. On the contrary, when theelectrode with the bias voltage is disposed on each of the first andsecond side surfaces of the vibrational arm, an alternating currentvoltage is applied between the electrode disposed opposite to the firstside surface of the vibrational arm and the electrode disposed oppositeto the second side surface of the vibrational arm. In other words, whenthe electrode disposed opposite to the electrode of the first sidesurface of the vibrational arm and the electrode of the first sidesurface of the vibrational arm are disposed so that an attractive forceoccurs between them, the electrode disposed opposite to the electrode ofthe second side surface of the vibrational arm and the electrode of thesecond side surface of the vibrational arm are disposed so that arepulsive force occurs between them, inversely, when the electrodedisposed opposite to the electrode of the first side surface of thevibrational arm and the electrode of the first side surface of thevibrational arm are disposed so that the repulsive force occurs betweenthem, the electrode disposed opposite to the electrode of the secondside surface of the vibrational arm and the electrode of the second sidesurface of the vibrational arm are disposed so that the attractive forceoccurs between them. As a result, the vibrational arm can vibrate in aflexural mode. In the electrode disposition of this embodiment shown inFIG. 28, the resonator can vibrate in a fundamental mode of a flexuralmode. In this embodiment, the resonator comprises a vibrational arm, butthe resonator of the present invention may comprise a plurality ofvibrational arms, e.g. a tuning fork shape comprising a tuning fork baseand first and second tuning fork arms connected to the tuning fork base,and the tuning fork base may have cut portions. In this case, aresonator of the tuning fork shape vibrates in a flexural mode,preferably, in the flexural mode of an inverse phase, and the electrodesto drive the flexural mode of the inverse phase are disposed similar tothe electrodes shown in FIG. 26 and FIG. 27 and similar to the mattersdescribed in FIG. 26 and FIG. 27. Moreover, the resonator of the tuningfork shape comprises a plurality of mounting frames having a first frameand a second frame which protrude from opposite side surfaces of thetuning fork base, respectively, and preferably, an end portion of thefirst frame is connected to an end portion of the second frame and thefirst and second frames are mounted on a mounting portion of a case orthe first and second frames are formed with the case integratedly. Inaddition, an oscillation frequency f of the flexural mode resonator isgenerally defined by f=KW/L², where W and L is a width and a length of avibrational arm, respectively, and K is basically determined by aboundary condition, an order of vibration and a material constant of theflexural mode resonator. According to the present invention, the width Whas a value of 0.001 mm to 0.045 mm, preferably, 0.003 mm to 0.035 mm,more preferably, 0.005 mm to 0.025 mm and a ratio W/L is within a rangeof 2×10⁻³ to 2.5×10⁻¹ to get an enough shock-proof and to achieve asmall-sized flexural mode resonator with a high quality factor. In orderto achieve a further small-sized flexural mode resonator with an enoughhigh quality factor, the width W has a value of less than 1 μm,preferably, greater than 0.35 μm because an oscillation frequency of theflexural mode resonator is proportional to the width W. In addition,when an output signal of an oscillating circuit comprising the flexuralmode resonator of one of the embodiments described above is used as aclock signal for use in operation of the electronic apparatus to displaytime information, the flexural mode resonator, preferably, comprises aclamped-free type resonator or a tuning fork type resonator and anoscillation frequency of the output signal is about 32.768 kHz with afrequency deviation within a range of −950 ppm to +950 ppm, preferably,−100 ppm to +100 ppm, more preferably, −50 ppm to +50 ppm. In moredetail, when the resonator has a nominal frequency of 32.768 kHz, thesmaller the frequency deviation to the nominal frequency becomes, thesmaller the time error of the output signal becomes, e.g. when thefrequency deviation has 10 ppm, the time error of the output signalbecomes about 26 seconds per a month in the calculation. According tothe present invention, the flexural mode resonator may comprise aboundary condition of “free-free”. In addition, the flexural moderesonator having the boundary condition of “clamped-clamped” or“clamped-free” or “free-free” described above is formed by an epitaxialgrowth method. Though a metal film is formed on neither an obverse faceor a reverse face opposite the obverse face of the flexural moderesonator shown in FIG. 26 or FIG. 28 to adjust an oscillation frequencythereof, the metal film is actually formed on at least one of theobverse and reverse faces of each of the vibrational arms or at leastone of the obverse and reverse faces of the vibrational arm of theflexural mode resonator to adjust the oscillation frequency thereof. Indetail, the oscillation frequency is adjusted by forming the metal filmon at least one of the obverse and reverse faces of each of thevibrational arms or by forming the metal film on at least one of theobverse and reverse faces of the vibrational arm or by trimming themetal film formed on at least one of the obverse and reverse faces ofeach of the vibrational arms or by trimming the metal film formed on atleast one of the obverse and reverse faces of the vibrational arm. As aresult of which, e.g. when the flexural mode resonator comprises theclamped-free type resonator, the clamped-free resonator has theoscillation frequency of about 32.768 kHz with the frequency deviationin the range of −950 ppm to +950 ppm or −100 ppm to +100 ppm or −50 ppmto +50 ppm. In addition, the flexural mode resonators shown in FIG. 26and FIG. 28 may be used as a sensor for sensing angular velocity orpressure or temperature. As a further another example, when the flexuralmode resonator comprises the clamped-clamped type resonator or thefree-free type resonator, the resonator has the oscillation frequencyhigher than 65 kHz to get the resonator small-sized. As a result ofwhich it is very easy to get an output signal with the oscillationfrequency in the range of 500 kHz to 150 MHz by construction of circuitsshown in FIG. 30 and FIG. 32 each of which will describe in detailbelow. A block diagram comprised of a plurality of circuits is shown inFIG. 30 to get an output signal according to the present invention. Theblock diagram comprises an oscillating circuit (OSC) 730, a buffercircuit (B/C), dividing circuits of frequency (frequency dividers) (1/R,1/N), a phase detector (P/D) and a voltage controlled oscillator (VCO).The OSC 730 comprises a resonator 732 and a temperature compensatedcircuit 731 having a varactor (varicap) diode, a capacitor and aresistor. Also, the resonator 732 comprises the clamped-clamped typeresonator capable of vibrating in a flexural mode shown in FIG. 26 orthe clamped-free type resonator capable of vibrating in a flexural modeshown in FIG. 28 or the free-free type resonator capable of vibrating ina flexural mode. In more detail, an output signal of the OSC 730 havingan oscillation frequency is output through the buffer circuit (B/C),namely, the oscillation frequency of the OSC 730 is the same as anoscillation frequency defined by p_(f) which is at a point p shown by anarrow and there is a relationship of a_(f)=p_(f)/R and b_(f)=c_(f)/N,where a_(f), b_(f) and c_(f) show an oscillation frequency which is atpoints a, b and c shown by arrows, respectively. Furthermore, there is arelationship of c_(f)=N×p_(f)/R by using the relation of a_(f)=b_(f). Indetail, a voltage of the VCO changes so that a_(f) is equal to b_(f)from information of the P/D. A block diagram comprising the dividingcircuits of frequency (frequency dividers) (1/R, 1/N), the phasedetector (P/D) and the voltage controlled oscillator (VCO) is defined bya phase locked loop (PLL) circuit here (in this invention). Thus, anoutput signal having the oscillation frequency c_(f) can be obtainedwith a high stability of frequency by comprising the PLL circuit of thisembodiment. For example, when p_(f) is 1 MHz, R is 10 and N is 1000,c_(f) has 100 MHz. As is apparent from this result, the output signalhaving an arbitrary oscillation frequency can be obtained by selectingN, R and p_(f) of the PLL circuit. Furthermore, the OSC comprises anamplification circuit having an amplifier (CMOS inverter) and a feedbackresistor, and a feedback circuit having the flexural mode resonator, adrain resistor, a plurality of capacitors and the temperaturecompensated circuit. Therefore, when the flexural mode resonator has acomparatively large first order temperature coefficient α_(t) e.g.1.5×10⁻⁵ to 3.2×10⁻⁵ in the absolute value, the first order temperaturecoefficient at reaches approximately zero by compensating the α_(t)using the temperature compensated circuit. As the result, the flexuralmode resonator can be obtained with good frequency temperature behavioure.g. frequency deviation of −30 ppm to +30 ppm in a wide temperaturerange of −30° C. to +80° C. because the second and third ordertemperature coefficients β_(t), γ_(t) get small in the absolute value,e.g. β_(t) is less than 1×10⁻⁷ in the absolute value and γ_(t) is lessthan 8×10⁻¹¹ in the absolute value, when the at is large comparatively.In addition, another block diagram comprised of a plurality of circuitsis shown in FIG. 31 to get a plurality of output signals according tothe present invention. The block diagram comprises an oscillatingcircuit (OSC) 740, a buffer circuit (B/C) and a dividing circuit offrequency (frequency divider) (1/R). The oscillating circuit (OSC) 740comprises a resonator 742 and a temperature compensated circuit 741.Also, the resonator 742 comprises the flexural mode resonator alreadydescribed in FIG. 30 and the OSC 740 comprises the amplification circuitand the feedback circuit of the OSC 730 already described in FIG. 30. Inthis embodiment, output 1 which is a first output signal is output fromthe OSC 740 through the buffer circuit and output 2 which is a secondoutput signal is output from the OSC 740 through the buffer circuit andthe dividing circuit. Like this, the first and second output signalseach having an oscillation frequency can be obtained and the oscillationfrequency of the first output signal is naturally different from that ofthe second output signal. In addition, a still another block diagramcomprised of a plurality of circuits is shown in FIG. 32 to get aplurality of output signals according to the present invention. Theblock diagram comprises an oscillating circuit (OSC) 750, a buffercircuit (B/C), a plurality of dividing circuits of frequency (aplurality of frequency dividers) (1/R, 1/N), a phase detector (P/D) anda voltage controlled oscillator (VCO). The OSC 750 comprises a resonator752 and a temperature compensated circuit 751. In other words, the blockdiagram comprises the OSC 750, the B/C, the dividing circuit offrequency (frequency divider) (1/R) and a PLL circuit. Also, theresonator 752 comprises the flexural mode resonator already described inFIG. 30 and the OSC 750 comprises the amplification circuit and thefeedback circuit of the OSC 730 already described in FIG. 30. Namely,each of the OSC 740 in FIG. 31 and the OSC 750 in FIG. 32 is the same asthe OSC 730 in FIG. 30. In this embodiment, output 1 which is a firstoutput signal is output from the OSC 750 through the B/C, output 2 whichis a second output signal is output from the OSC 750 through the buffercircuit and the dividing circuit, and output 3 which is a third outputsignal is output from the OSC 750 through the buffer circuit and the PLLcircuit. Thus, the first, second and third output signals can beobtained with an oscillation frequency different, respectively, byconstruction of the circuits of FIG. 32. In the embodiments, theelectrostatic force is used to get the attractive force and therepulsive force between the opposite side surfaces, but according to thepresent invention, a magnetic force may be used instead of theelectrostatic force. Namely, the attractive force can be obtained by twodifferent magnetic poles, e.g. N-S poles or S-N poles, while therepulsive force can be obtained by two same magnetic poles, e.g. N-Npoles or S-S poles. In addition, it is needless to say that the presentinvention includes the flexural mode resonator capable of vibrating in aflexural mode by a combination of the electrostatic force and themagnetic force. Also, the clamped-clamped type resonator, theclamped-free type resonator and the free-free type resonator shown inthe embodiments of the present invention may be called a clamped-clampedbeam resonator, a clamped-free beam resonator and a free-free beamresonator, respectively.

FIG. 8 a and FIG. 8 b are a top view and a side view for alength-extensional mode quartz crystal resonator which is one of acontour mode resonator, constructing a quartz crystal oscillator, whichconstructs an electronic apparatus of the third embodiment of thepresent invention. The resonator 62 comprises a vibrational portion 63,connecting portions 66, 69 and supporting portions 67, 80 includingrespective mounting portions 68, 81. In addition, the supportingportions 67 and 80 have respective holes 67 a and 80 a. Also, electrodes64 and 65 are disposed opposite each other on upper and lower faces ofthe vibrational portion 63, and the electrodes have opposite electricalpolarities. Namely, a pair of electrodes is disposed on the vibrationalportion. In this case, a fundamental mode vibration can be excitedeasily. In more detail of this embodiment, the resonator 62 has thevibrational portion 63, first and second supporting portions 67, 80, andfirst and second connecting portion 66, 69. Namely, the first supportingportion is connected to the vibrational portion through the firstconnecting portion, and the second supporting portion is connected tothe vibrational portion through the second connecting portion, so thattwo supporting portions are constructed. Therefore, the two supportingportions may have the first supporting portion and the second supportingportion connected each other, namely, it is needless to say that thesupporting portions of the present invention include the supportingportions connected each other.

In addition, the electrode 64 extends to the mounting portion 81 throughthe one connecting portion 69 and the electrode 65 extends to themounting portion 68 through the other connecting portion 66. In thisembodiment, the electrodes 64 and 65 disposed on the vibrational portion63 extend to the mounting portions of the different direction eachother. But, the electrodes may be constructed in the same direction. Theresonator in this embodiment is mounted on fixing portions of a case ora lid at the mounting portions 68 and 81 by conductive adhesives orsolder.

Here, a cutting angle of the length-extensional mode quartz crystalresonator is shown. First, a quartz crystal plate perpendicular to xaxis, so called, X plate quartz crystal is taken. Length L₀, width W₀and thickness T₀ which are each dimension of the X plate quartz crystalcorrespond to the respective directions of y, z and x axes.

Next, this X plate quartz crystal is, first, rotated with an angle θ_(x)of −30° to +30° about the x axis, and second, rotated with an angleθ_(y) of −40° to +40° about y′ axis which is the new axis of the y axis.In this case, the new axis of the x axis changes to x′ axis and the newaxis of the z axis changes to z″ axis because the z axis is rotatedtwice about two axes. The length-extensional mode quartz crystalresonator of the present invention is formed from the quartz crystalplate with the rotation angles.

In other words, according to an expression of IEEE notation, a cuttingangle of the resonator of the present invention can be expressed byXYtl(−30° to +30°)/(−40° to +40°). By choosing a cutting angle of theresonator, a turn over temperature point T_(p) can be taken at anarbitrary temperature. In this embodiment, length L₀, width W₀ andthickness T₀ correspond to y′, z″ and x′ axes, respectively. But, whenthe X plate is rotated once about the x axis, the z″ axis corresponds tothe z′ axis. In addition, the vibrational portion 63 has a dimension oflength L₀ greater than width W₀ and thickness T₀ smaller than the widthW₀. Namely, a coupling between length-extensional mode andwidth-extensional mode gets so small as it can be ignored, as a resultof which, the quartz crystal resonator can vibrate in a singlelength-extensional mode.

In more detail, resonance frequency of the length-extensional moderesonator is inversely proportional to length L₀, and it is almostindependent on such an other dimension as width W₀, thickness T₀,connecting portions and supporting portions. Also, in order to obtain alength-extensional mode quartz crystal resonator capable of vibrating ina fundamental mode with a frequency of 1 MHz to 10 MHz, the length L₀ iswithin a range of about 0.26 mm to about 2.7 mm. In addition, when alength-extensional mode resonator vibrates in an overtone mode, an oddnumber (n) pair of electrodes are disposed on a vibrational portion ofthe resonator, where n has a value of 1, 3, 5, . . . . In this case, thelength L₀ is within a range of about (0.26 to 2.7) x n mm. Thus, theminiature length-extensional mode resonator can be provided with thefrequency of 1 MHz to 10 MHz. In addition, FIG. 18 shows a relationshipbetween a dimensional ratio R=W₀/L₀ and a cut angle θ_(x) of thelength-extensional mode quartz crystal resonator to give a zerotemperature coefficient, namely, when the ratio R is in the range of0.325 to 0.475 and the cut angle θ_(x) is in the range of about 7° toabout 22°, there are many zero temperature coefficients, where the cutangle θ_(x) is defined by XYt(θ_(x)) according to an expression of theIEEE notation. In addition, when the ratio R is in the range of 0.3 to0.325 and 0.475 to 0.5, and the cut angle θ_(x) is in the range of 6° to7° and 22° to 23°, there is a small first order temperature coefficient.Therefore, in order to get a turn over temperature point over a widetemperature range, the ratio R is in the range of 0.3 to 0.5, the cutangle of the resonator is within a range of XYt(6° to 23°).

Next, a value of a piezoelectric constant e₁₂ (=e′₁₂) is described,which is of great importance and necessary to excite a flexural mode,quartz crystal resonator and a length-extensional mode quartz crystalresonator of the present invention. The larger a value of thepiezoelectric constant e₁₂ becomes, the higher electromechanicaltransformation efficiency becomes. The piezoelectric constant e₁₂ of thepresent invention can be calculated using the piezoelectric constantse₁₁=0.171 C/m² and e₁₄=−0.0406 C/m² of quartz crystal. As a result, thepiezoelectric constant e₁₂ of the present invention is within a range of0.095 C/m² to 0.19 C/m² approximately in an absolute value. It is,therefore, easily understood that this value is enough large to obtain aflexural mode, quartz crystal tuning fork resonator and alength-extensional mode quartz crystal resonator with a small seriesresistance R₁ and a high quality factor Q. Especially, in order toobtain a flexural mode, quartz crystal tuning fork resonator with asmaller series resistance R_(t), the e₁₂ is within a range of 0.12 C/m²to 0.19 C/m² in the absolute value, and also, a groove and electrodesare provided on at least one of an obverse face and a reverse face oftuning fork tines so that when each tuning fork tine is divided into twoportions (an inner portion located at a fork side and an outer portionlocated opposite to the fork side) versus a central line portionthereof, a value of e₁₂ of each portion of each tuning fork tine has anopposite sign each other. Namely, when the one of the two portions hase₁₂ of a plus sign, the other of the two portions has e₁₂ of a minussign. In more detail, a groove and electrodes are provided at tuningfork tines so that a sign of e₁₂ of inner portions of each tuning forktine is opposite to the sign of e₁₂ of outer portions of each tuningfork tine.

When an alternating current voltage is applied between the electrodes 64and 65 shown in FIG. 8 b, an electric field E_(x) occurs alternately inthe thickness direction, as shown by the arrow direction of the solidand broken lines in FIG. 8 b. Consequently, the vibrational portion 63is capable of extending and contracting in the length direction.

FIG. 9 shows a cross-sectional view of a quartz crystal unitconstructing a quartz crystal oscillator, which constructs an electronicapparatus of the fourth embodiment of the present invention. The quartzcrystal unit 170 comprises a contour mode quartz crystal resonator 70 ora thickness shear mode quartz crystal resonator 70, a case 71 and a lid72. In more detail, the resonator 70 is mounted at a mounting portion 74of the case 71 by conductive adhesives 76 or solder. Also, the case 71and the lid 72 are connected through a connecting member 73. Forexample, the contour mode resonator 70 in this embodiment is the sameresonator as one of the flexural mode, quartz crystal tuning forkresonators 10 and 45 described in detail in FIG. 4-FIG. 7. Also, in thisembodiment, circuit elements are connected at outside of the quartzcrystal unit to get a quartz crystal oscillator. Namely, only the quartzcrystal tuning fork resonator is housed in the unit and also, it ishoused in the unit in vacuum. In this embodiment, the quartz crystalunit of a surface mounting type is shown, but the quartz crystal tuningfork resonator may be housed in a unit of a tubular type, namely aquartz crystal unit of the tubular type. In other words, the quartzcrystal unit of the tubular-type has a case having two lead wires whichare a mounting portion of the case to mount the quartz crystal tuningfork resonator, and an open end of the case is connected to a lid tocover the open end of the case. Also, instead of the flexural mode,quartz crystal tuning fork resonator and the thickness shear mode quartzcrystal resonator, one of a length-extensional mode quartz crystalresonator, a width-extensional mode quartz crystal resonator and a Lamemode quartz crystal resonator which are a contour mode resonator,respectively, or a SAW (Surface Acoustic Wave) resonator may be housedin the unit. For example, FIG. 19 shows a top view (a) and a C-C′cross-sectional view (b) of a vibrational portion 555 of a thicknessshear mode quartz crystal resonator 550. The resonator 550 has adimension of a length L₀, a width W₀ and a thickness T₀, and the lengthL₀ and the width W₀ is less than 2.4 mm and 1.6 mm, respectively, toachieve a smaller quartz crystal unit and to get a small seriesresistance R₁. Also, electrodes 556 and 557 are disposed on upper andlower surfaces so that the electrodes are opposite each other. In orderto get a good frequency temperature behaviour at a room temperature atleast, the resonator 550 has a cut angle within a range of YXl(34° to36°) according to an expression of the IEEE notation. In addition, thepresent invention is not limited to the quartz crystal unit having thecontour mode quartz crystal resonator or the thickness shear mode quartzcrystal resonator in this embodiment, for example, the present inventionalso includes a quartz crystal unit having a piezoelectric filter, e.g.a SAW piezoelectric filter or a piezoelectric sensor, e.g. an angularvelocity piezoelectric sensor. Namely, the piezoelectric materialcomprises one of LiTaO₃, LiNbO₃, GaPO₄, and so on which belong to atrigonal system in crystallographic classification.

In addition, a member of the case and the lid is ceramics or glass and ametal or glass, respectively, and a connecting member is a metal orglass with low melting point. Also, a relationship of the resonator, thecase and the lid described in this embodiment is applied to a quartzcrystal oscillator of the present invention which will be described inFIG. 10.

FIG. 10 shows a cross-sectional view of a quartz crystal oscillator,which constructs an electronic apparatus of the fifth embodiment of thepresent invention. The quartz crystal oscillator 190 comprises a quartzcrystal oscillating circuit, a case 91 and a lid 92. In this embodiment,circuit elements constructing the oscillating circuit are housed in aquartz crystal unit comprising a contour mode quartz crystal resonator90 or a thickness shear mode quartz crystal resonator 90, the case 91and the lid 92. Also, the oscillating circuit of this embodimentcomprises an amplifier 98 including a feedback resistor, the resonator90, capacitors (not shown here) and a drain resistor (not shown here),and a CMOS inverter is used as the amplifier 98.

In addition, in this embodiment, the resonator 90 is mounted at amounting portion 94 of the case 91 by conductive adhesives 96 or solder.As described above, the amplifier 98 is housed in the quartz crystalunit and mounted at the case 91. Also, the case 91 and the lid 92 areconnected through a connecting member 93. For example, the contour moderesonator 90 of this embodiment is the same as one of the flexural mode,quartz crystal tuning fork resonators 10 and 45 described in detail inFIG. 4-FIG. 7. Also, instead of the flexural mode, quartz crystal tuningfork resonator and the thickness shear mode quartz crystal resonator,one of a length-extensional mode quartz crystal resonator, awidth-extensional mode quartz crystal resonator and a Lame mode quartzcrystal resonator which are a contour mode resonator, respectively, or aSAW (Surface Acoustic Wave) resonator, or a torsional mode quartzcrystal resonator may be housed in the unit. In addition, the torsionalmode resonator has a tuning fork shape with a tuning fork base havingcut portions and tuning fork tines connected to the tuning fork base.The tuning fork tines vibrate in a torsional mode of an inverse. Inaddition, a length of each of the tuning fork tines is within a range of0.6 mm to 2.1 mm, preferably, 0.65 mm to 1.85 mm, so that the torsionalresonator capable of vibrating in a fundamental mode can be obtainedwith a frequency higher than 150 kHz and less than 750 kHz.

Likewise, in this embodiment, a piece of flexural mode, quartz crystaltuning fork resonator is housed in the unit, but the present inventionalso includes a quartz crystal unit having a plurality of flexural mode,quartz crystal tuning fork resonators, each of which has tuning forktines and a tuning fork base, and at least two of the plurality ofresonators are connected electrically in parallel. In addition, the atleast two resonators may be an individual resonator or may be individualresonators that are formed integrally at each tuning fork base through aconnecting portion. For example, the at least two resonators comprisestwo individual resonators, and the two individual resonators are formedso that one of the two individual resonators has a groove in at leastone of upper and lower faces of the tuning fork tines, and the other hasno groove in at least one of upper and lower faces of the tuning forktines to get a different turn over temperature point each other. Inaddition, a shape and a dimension of the groove and the tuning forktines may be changed to get the different turn over temperature pointeach other.

Next, a method for manufacturing a quartz crystal oscillator, whichconstructs an electronic apparatus of the present invention, isdescribed in detail, according to the manufacturing steps.

FIG. 11 shows an embodiment of a method for manufacturing a quartzcrystal oscillator, which constructs an electronic apparatus of thepresent invention and a step diagram embodying the present invention.The signs of S-1 to S-12 are the step numbers. First, S-1 shows across-sectional view of a quartz crystal wafer 140. Next, in S-2 a metalfilm 141, for example, chromium and gold on the chromium are,respectively, disposed on upper and lower faces of the quartz crystalwafer 140 by an evaporation method or a spattering method. In addition,a resist 142 is spread on said metal film 141 in S-3, and after themetal film 141 and the resist 142 are removed except those of tuningfork shape by a photo-lithographic process and an etching process, thetuning fork shape with tuning fork tines 143, 144 and a tuning fork base145, as be shown in S-4, is integrally formed by a chemical etchingprocess, namely, in a first etching process so that an oscillationfrequency of a quartz crystal resonator of the tuning fork shape whichis a first oscillation frequency, is in the range of 33.8 kHz to 40 kHz,preferably, 34.1 kHz to 38.7 kHz, more preferably, 34.1 kHz to 36.9 kHz.When the tuning fork shape is formed, cut portions may be formed at thetuning fork base. In other words, the tuning fork shape and the cutportions are formed simultaneously. In FIG. 11, the formation of a pieceof tuning fork shape is shown, but, a number of tuning fork shapes areactually formed in a piece of quartz crystal wafer.

Similar to the steps of S-2 and S-3, a metal film and a resist arespread again on the tuning fork shape of S-4 and grooves 146, 147, 148and 149 each of which has two stepped portions including a first steppedportion and a second stepped portion opposite the first stepped portionin the width direction along the length direction of the tuning forktines, are formed at the tuning fork tines 143, 144 by thephoto-lithographic process and the etching process, namely, in a secondetching process different from the first etching process so that theoscillation frequency of the quartz crystal resonator of the tuning forkshape having the grooves which is a second (or first) oscillationfrequency, is in the range of 32.78 kHz to 34.9 kHz, preferably, 32.78kHz to 34.4 kHz, more preferably, 32.78 kHz to 33.85 kHz and a turn overtemperature point (turning point) of the quartz crystal resonatorthereof is in the range of 15° C. to 35° C., preferably, 18° C. to 30°C. to get a small frequency deviation in the vicinity of roomtemperature because the quartz crystal resonator of the tuning forkshape has a parabolic curve in frequency temperature behaviour, and theshape of S-5 is obtained after all of the resist and the metal film areremoved. In order to obtain the small motional inductance L₁ of thefundamental mode vibration, it is needless to say that the grooves 146,147, 148 and 149 have the depth t₁ and the depth t₂ larger than 0.021mm, preferably, larger than 0.025 mm and less than 0.075 mm, morepreferably, larger than 0.03 mm and less than 0.055 mm asabove-described. In addition, a metal film and a resist are spread againon the shape of S-5 and electrodes which are of opposite electricalpolarity, are disposed on sides of the tines and inside the groovesthereof, as be shown in S-6.

Namely, electrodes 150, 153 disposed on the sides of the tuning forktine 143 and electrodes 155, 156 disposed inside the grooves 148, 149 ofthe tuning fork tine 144 have the same electrical polarity. Similarly,electrodes 151, 152 disposed inside the grooves 146, 147 of the tuningfork tine 143 and electrodes 154, 157 disposed on the sides of thetuning fork tine 144 have the same electrical polarity. Two electrodeterminals are, therefore, constructed. In more detail, when analternating current (AC) voltage is applied between the terminals, thetuning fork tines vibrate in a flexural mode of an inverse phase becausesaid electrodes disposed on the stepped portions of the grooves and theelectrodes disposed opposite to the said electrodes have oppositeelectrical polarity. In the step of S-6, a piece of quartz crystaltuning fork resonator, capable of vibrating in a flexural mode is shownin the quartz crystal wafer, but a number of quartz crystal tuning forkresonators are actually formed in the quartz crystal wafer. When thegrooves are formed at the tuning fork tines, the oscillation frequencyof the resonator of the tuning fork shape becomes lower than that of theresonator with no groove, and the quantity of a change of theoscillation frequency is dependent on a number of the grooves, a groovewidth, a groove length and a groove depth. In this embodiment, theoscillation frequency of the resonator of the tuning fork shape isadjusted in the quartz crystal wafer by forming a metal film on each ofat least two of the upper and lower faces of each of the tuning forktines so that the oscillation frequency which is a third (or second)oscillation frequency is lower than 32.73 kHz, preferably, less than32.69 kHz, more preferably, greater than 31.6 kHz and less than 32.69kHz and the metal film is formed after or before the step of S-6,namely, after or before the two electrode terminals are formed to drivethe resonator of the tuning fork shape. In more detail, the metal filmon each of at least two of the upper and lower faces of each of thetuning fork tines to adjust the oscillation frequency is formed afterthe tuning fork shape is formed (after the step of S-4) and before thegrooves are formed (before the step of S-5) or is formed after thegrooves are formed (after the step of S-5) and before the electrodes aredisposed (before the step of S-6) or is formed after the electrodes aredisposed (after the step of S-6) and before the resonator of the tuningfork shape is mounted on a mounting portion of a case (before the stepof S-7 or S-8). Also, when the resonator of the tuning fork shape housedin a unit having a case and a lid has no groove at the tuning forktines, an oscillation frequency of the resonator of the tuning forkshape formed in a quartz wafer by etching is in the range of 32.78 kHzto 34.9 kHz, preferably, 32.78 kHz to 34.4 kHz, more preferably, 32.78kHz to 33.85 kHz. In addition, a metal film on each of at least two ofthe upper and lower faces of each of the tuning fork tines is formed toadjust the oscillation frequency of the resonator so that theoscillation frequency is lower than 32.73 kHz, preferably, less than32.69 kHz, more preferably, greater than 31.6 kHz and less than 32.69kHz, and the metal film is formed after or before the electrodes (twoelectrode terminals) are formed to drive the resonator of the tuningfork shape. In more detail, the metal film on each of at least two ofthe upper and lower faces of each of the tuning fork tines is formedafter the tuning fork shape is formed and before the electrodes aredisposed or is formed after the electrodes are disposed and before thetuning fork shape is mounted on a mounting portion of a case. Accordingto the present invention, the metal film on each of at least two of theupper and lower faces of each of the tuning fork tines may be formedbefore the tuning fork shape is formed.

In addition, the oscillation frequency of the resonator of the tuningfork shape is adjusted to get a fourth (or third) oscillation frequencyand a fifth (or fourth) oscillation frequency by separate steps of atleast twice and a first adjustment of the oscillation frequency of theresonator is performed in the quartz crystal wafer to get the fourth (orthird) oscillation frequency by a laser method or an evaporation methodor an ion etching method so that a frequency deviation of the resonatoris within a range of −9000 PPM to +5000 PPM (Parts Per Million),preferably, within a range of −9000 PPM to +100 PPM, more preferably,within a range of −2300 PPM to +100 PPM to a nominal frequency of 10 kHzto 200 kHz, e.g. 32.768 kHz. The first adjustment of the oscillationfrequency by the laser method or the ion etching method is performed bytrimming mass (e.g. the metal films) disposed on tuning fork tines andthe first adjustment of the oscillation frequency by the evaporationmethod is performed by adding mass (e.g. a metal) on tuning fork tines.Namely, those methods can change the oscillation frequency of saidresonator. Also, the resonators formed in the quartz crystal wafer areinspected therein and when there is a failure (damaged) resonator, it isremoved from the wafer or something is marked on it or it is rememberedby a computer.

In this embodiment, the tuning fork shape is formed from the step of S-3and after that, the grooves are formed at the tuning fork tines, namely,the tuning fork tines are formed before the grooves are formed, but thisinvention is not limited to said embodiment, for example, the groovesare first formed from the step of S-3 and after that, the tuning forkshape may be formed, namely, the grooves are formed before the tuningfork tines are formed. Also, the tuning fork shape and the grooves maybe formed simultaneously, namely, the tuning fork tines and the groovesare formed simultaneously. When the tuning fork tines and the groovesare formed simultaneously, for example, a portion between the tuningfork tines is first etched so that the portion has a groove and athickness of the portion is less than seven tenths, preferably, one halfof a thickness of the quartz crystal wafer to get a required oscillationfrequency and a required turn over temperature point, and after that,both of the portion and the groove are formed simultaneously by etchingthe quartz crystal wafer. For example, when the thickness of the quartzcrystal wafer is in the range of 0.07 mm to 0.12 mm, the thickness ofthe base portion is less than 0.05 mm, preferably, 0.035 mm, morepreferably, 0.005 mm. Namely, the portion has the groove as deep aspossible to get the required oscillation frequency and the required turnover temperature point. Moreover, when the tuning fork base has cutportions, the portion between the tuning fork tines and the cut portionsare formed simultaneously. In addition, when the tuning fork base has aframe portion, the tuning fork shape and the frame portion are formedsimultaneously. According to the present invention, when the tuning forkbase has at least one of cut portions and a frame portion, the at leastone is formed simultaneously with the tuning fork shape. Moreover, forexample, when a groove having a plurality of stepped portions is formedin each of upper and lower faces of the tuning fork tines, the groovemay be formed simultaneously with at least one of the cut portions andthe frame portion. In addition, at least one of the cut portions may beformed in a step different from at least one of the steps of forming thetuning fork tines and forming the grooves at the tuning fork tines.Namely, the at least one of the cut portions is formed before or afterat least one of the tuning fork tines and the grooves is formed. Similarto this, the frame portion may be formed in a step different from atleast one of the steps of forming the tuning fork tines and forming thegrooves at the tuning fork tines. Namely, the frame portion is formedbefore or after at least one of the tuning fork tines and the grooves isformed. In addition, at least one of the metal films on the upper andlower faces of each of the tuning fork tines to adjust the oscillationfrequency of the resonator of the tuning fork shape may be formed beforethe step of forming the tuning fork tines. Also, the grooves are formedbefore the tuning fork tines are formed and after that, when the tuningfork tines are formed, the quartz crystal resonator of the tuning forkshape has an oscillation frequency in the range of 32.78 kHz to 34.9kHz, preferably, 32.78 kHz to 34.4 kHz, more preferably, 32.78 kHz to33.85 kHz and a turn over temperature point (turning point) of thequartz crystal resonator thereof is in the range of 15° C. to 35° C.,preferably, 18° C. to 30° C. In addition, when the tuning fork tines andthe grooves are formed simultaneously, the quartz crystal resonator ofthe tuning fork shape has an oscillation frequency in the range of 32.78kHz to 34.9 kHz, preferably, 32.78 kHz to 34.4 kHz, more preferably,32.78 kHz to 33.85 kHz and a turn over temperature point (turning point)of the quartz crystal resonator thereof is in the range of 15° C. to 35°C., preferably, 18° C. to 30° C.

There are two methods of A and B in the following step, as be shown byarrow signs. For the step of A, the tuning fork base 145 of the formedflexural mode, quartz crystal tuning fork resonator 160 is first mountedon a mounting portion 159 of a case 158 by conductive adhesives 161 orsolder, as be shown in S-7. Next, a second adjustment of the oscillationfrequency for the resonator 160 is performed to get the fifth (orfourth) oscillation frequency by a laser method 162 or an evaporationmethod or an ion etching method in S-8 so that a frequency deviation iswithin a range of −100 PPM to +100 PPM to the nominal frequency of 10kHz to 200 kHz, e.g. 32.768 kHz. Finally, the case 158 and a lid 163 areconnected via glass 164 with the low melting point or a metal in S-9. Inthis case, the connection of the case and the lid is performed in vacuumbecause the case 158 has no hole to close it in vacuum.

In addition, though it is not visible in FIG. 11, a third adjustment ofthe oscillation frequency may be performed by the laser method after thestep of the connection of S-9 to get a small frequency deviation to thenominal frequency when a material of the lid is glass. As a result ofwhich it is possible to get the resonator with the frequency deviationwhich is within a range of −50 PPM to +50 PPM to the nominal frequencyof 10 kHz to 200 kHz, e.g. 32.768 kHz. Namely, the nominal frequency ofthe resonator capable of vibrating in a fundamental mode is less than200 kHz. In this step, when the third adjustment of the oscillationfrequency is performed, the oscillation frequency of the resonator isadjusted so that the frequency deviation of the resonator adjusted bythe second adjustment of the oscillation frequency is within a range of−1500 PPM to +1500 PPM, preferably, −950 PPM to +950 PPM to the nominalfrequency, e.g. 32.768 kHz.

For the step of B, the tuning fork base 145 of the formed resonator 160is first mounted on a mounting portion 159 of a case 165 by conductiveadhesives 161 or solder in S-10, in addition, in S-11 the case 165 and alid 163 are connected by the same way as that of S-9, in more detail,after the resonator is mounted on the mounting portion of the case orafter the resonator is mounted at the mounting portion, and the case andthe lid are connected, the second adjustment of the oscillationfrequency of the resonator is performed to get the fifth (or fourth)oscillation frequency so that a frequency deviation is generally withina range of −100 PPM to +100 PPM to a nominal frequency of 10 kHz to 200kHz, e.g. 32.768 kHz in vacuum, but, it may be within a wider range, forexample, −950 PPM to +950 PPM when the third adjustment of theoscillation frequency as will be shown as follows, is performed.Finally, a hole 167 constructed at the case 165 is closed in vacuumusing such a metal 166 as solder or glass with the low melting point inS-12.

Also, similar to the step of A, the third adjustment of the oscillationfrequency may be performed by the laser method after the step of S-12 toget a small frequency deviation to the nominal frequency. As a result ofwhich it is possible to get the resonator with the frequency deviationwhich is within a range of −50 PPM to +50 PPM to the nominal frequency,e.g. 32.768 kHz. Thus, the frequency deviation of each of the resonatorsin the case of the steps of A and B is finally within a range of −100PPM to +100 PPM at most. Also, the second adjustment of the oscillationfrequency may be performed after the case and the lid are connected andthe hole is closed in vacuum. In addition, the hole is constructed atthe case, but may be constructed at the lid. Also, the adjustment of theoscillation frequency of the present invention is performed in vacuum orinert gas such as nitrogen gas or atmosphere, and the values describedabove are values in vacuum. Furthermore, the oscillation frequency ofthe quartz crystal resonator of the tuning fork shape comprises thefirst, second, third, fourth and fifth (or the first, second, third andfourth) oscillation frequencies different each other.

Therefore, the flexural mode, quartz crystal tuning fork resonators andthe quartz crystal units manufactured by the above-described method areminiaturized and realized with a small series resistance R₁, a highquality factor Q₁ and low price.

Moreover, in the above-described embodiment, though the first frequencyadjustment of the resonators is performed in the quartz crystal waferand at the same time, when there is a failure resonator, something ismarked on it or it is removed from the quartz crystal wafer, but thepresent invention is not limited to this, namely, the present inventionmay include the step to inspect the flexural mode, quartz crystal tuningfork resonators formed in the quartz crystal wafer therein, in otherwords, the step to inspect whether there is a failure resonator or notin the quartz crystal wafer. When there is a failure resonator in thewafer, something is marked on it or it is removed from the wafer or itis remembered by a computer. By including the step, it can increase theyield because it is possible to find out the failure resonator in anearly step and the failure resonator does not go to the next step. As aresult of which low priced flexural mode, quartz crystal tuning forkresonators can be provided with excellent electrical characteristics.

In this embodiment, the frequency adjustment is performed three times inseparate steps, but may be performed at least twice in separate steps.For example, the third adjustment of the oscillation frequency may beomitted. In addition, in order to construct a quartz crystal oscillator,two electrode terminals of the resonators are connected electrically toan amplifier, capacitors and resistors. In other words, a quartz crystaloscillating circuit is constructed and connected electrically so that anamplification circuit comprises a CMOS inverter and a feedback resistorand a feedback circuit comprises a flexural mode, quartz crystal tuningfork resonator, a drain resistor, a capacitor of a gate side and acapacitor of a drain side. Also, the third adjustment of the oscillationfrequency may be performed after the quartz crystal oscillating circuitis constructed in a quartz crystal unit.

Likewise, the flexural mode quartz crystal resonator of the tuning forktype has two tuning fork tines in the present embodiments, butembodiments of the present invention include tuning fork tines more thantwo. In addition, the quartz crystal tuning fork resonators of thepresent embodiments are housed in a package (unit) of a surface mountingtype comprising a case and a lid, but may be housed in a package of atubular type.

In addition, for the tuning fork resonators constructing the quartzcrystal oscillators of the first embodiment to the fourth embodiment ofthe present invention, the resonators are provided so that a capacitanceratio r₁ of a fundamental mode vibration gets smaller than a capacitanceratio r₂ of a second overtone mode vibration, in order to obtain afrequency change of the fundamental mode vibration larger than that ofthe second overtone mode vibration, versus the same change of a value ofload capacitance C_(L). Namely, a variable range of a frequency of thefundamental mode vibration gets wider than that of the second overtonemode vibration.

In more detail, for example, when C_(L)=18 pF and the C_(L) changes in 1pF, the frequency change of the fundamental mode vibration becomeslarger than that of the second overtone mode vibration because thecapacitance ratio r₁ is smaller than the capacitance ratio r₂.Therefore, there is a remarkable effect for the fundamental modevibration, such that the resonators can be provided with the frequencyvariable in the wide range, even when the value of load capacitanceC_(L) changes slightly. Accordingly, when a variation of the samefrequency is required, the number of capacitors which are used in thequartz crystal oscillators decreases because the frequency change versusload capacitance 1 pF becomes large, as compared with that of the secondovertone mode vibration. As a result, the low priced oscillators can beprovided.

Moreover, capacitance ratios r₁ and r₂ of a flexural mode, quartzcrystal tuning fork resonator are given by r₁=C₀/C₁ and r₂=C₀/C₂,respectively, where C₀ is shunt capacitance in an electrical equivalentcircuit of the resonator, and C₁ and C₂ are, respectively, a motionalcapacitance of a fundamental mode vibration and a second overtone modevibration in the electrical equivalent circuit of the resonator. Namely,the relationship of r₁ less than r₂ implies that the motionalcapacitance C₁ of the fundamental mode of vibration is greater than themotional capacitance C₂ of the second overtone mode of vibration. Inaddition, the flexural mode, quartz crystal tuning fork resonator has aquality factor Q₁ for the fundamental mode vibration and a qualityfactor Q₂ for the second overtone mode vibration.

In detail, the tuning fork resonator of this embodiment is provided sothat the influence on resonance frequency of the fundamental modevibration by the shunt capacitance becomes smaller than that of thesecond overtone mode vibration by the shunt capacitance, namely, so thatit satisfies a relationship of S₁=r₁/2Q₁ ²<S₂=r₂/2Q₂ ², preferably,S₁<S₂/2. As a result, the tuning fork resonator, capable of vibrating inthe fundamental mode and having a high frequency stability can beprovided because the influence on the resonance frequency of thefundamental mode vibration by the shunt capacitance becomes so extremelysmall as it can be ignored. Also, the present invention replaces r₁/2Q₁² with S₁ and r₂/2Q₂ ² with S₂, respectively, and here, S₁ and S₂ arecalled “a stable factor of frequency” of the fundamental mode vibrationand the second overtone mode vibration.

In addition, when a power source is applied to the quartz crystaloscillating circuit, at least one oscillation which satisfies anamplitude condition and a phase condition of vibration starts in thecircuit, and a spent time to get to about ninety percent of the steadyamplitude of the vibration is called “rise time”. Namely, the shorterthe rise time becomes, the easier the oscillation becomes. When risetime t_(r1) of the fundamental mode vibration and rise time t_(r2) ofthe second overtone mode vibration in the circuit are taken, t_(r1) andt_(r2) are given by t_(r1)=kQ₁/(ω₁(−1+|−RL₁|/R₁)) andt_(r2)=kQ₂/(ω₂(−1+|−RL₂|/R₂)), respectively, where k is constant and ω₁and ω₂ are an angular frequency for the fundamental mode vibration andthe second overtone mode vibration, respectively. In addition, t_(r1)and t_(r2) can be expressed so that t_(r1)=kL₁/(|−RL₁|−R₁) andt_(r2)=kL₂/(|−RL₂|−R₂) using the relationships of Q₁/ω₁=L₁/R₁ andQ₂/ω₂=L₂/R₂, where L₁ and L₂ show a motional inductance of thefundamental mode vibration and the second overtone mode vibration,respectively, in the electrical equivalent circuit of the resonator.Also, when first rise time Tr₁ and second rise time Tr₂ are,respectively, defined by Tr₁=L₁/(|−RL₁|−R₁) and Tr₂=L₂/(|−RL₂|−R₂),t_(r1) and t_(r2) are, respectively, given by t_(r1)=kTr₁ andt_(r2)=kTr₂.

From the above-described relation, it is possible to obtain the risetime t_(r1) of the fundamental mode vibration less than the rise timet_(r2) of the second overtone mode vibration. As a result, the tuningfork resonator can vibrate in the fundamental mode very easily in theoscillating circuit because the rise time t_(r1) of the fundamental modevibration becomes shorter than the rise time t_(r2) of the secondovertone mode vibration. Also, it is needless to say that the first risetime Tr₁ is less than the second rise time Tr₂ from the relation of therise time t_(r1) less than the rise time t_(r2). As an example, whenresonance (oscillation) frequency of a flexural mode, quartz crystaltuning fork resonator is about 32.768 kHz for a fundamental modevibration and the resonator has a value of W₂/W=0.5, t₁/t=0.34 andl₁/l=0.48, though there is a distribution in production, as an example,the resonator has a value of Q₁=62,000 and Q₂=192,000, respectively. Inthis embodiment, Q₂ has a value of about three times of Q₁. Accordingly,to obtain the t_(r1) less than the t_(r2), it is necessary to satisfy arelationship of |−RL₁|/R₁>2|−RL₂ |/R₂−1 by using a relation of ω₂=6ω₁approximately. Also, according to this invention, the relationship isnot limited to the quartz crystal oscillating circuit comprising theresonator in this embodiment, but this invention also includes allquartz crystal oscillating circuits to satisfy the relationship. Byconstructing the oscillating circuit like this, a quartz crystaloscillator with the flexural mode, quartz crystal tuning fork resonatorcan be provided with a short rise time. In other words, an output signalof the oscillator has an oscillation frequency of the fundamental modevibration of the resonator and is outputted through a buffer circuit.Namely, the second overtone mode vibration can be suppressed in theoscillating circuit. In this embodiment, the resonator has also a valueof r₁=320 and r₂=10,600 as an example. According to this invention, r₁has a value of 210 to 520. In addition, the capacitance ratios r₁ and r₂can be rewritten so that r₁=C₀ω₁ ²L₁ and r₂=C₀ω₂ ²L₂ using the motionalinductance L₁ of the fundamental mode vibration and the motionalinductance L₂ of the second overtone mode vibration. Therefore, a ratio(L₁/L₂) of the motional inductance L₁ of the fundamental mode vibrationand the motional inductance L₂ of the second overtone mode vibration isless than 36 approximately from the relations of r₁ less than r₂ andω₂=6ω₁ approximately. Also, the ratio (L₁/L₂) is less than 6((Q₁/Q₂)from the relation of R₁<R₂, preferably, less than 5.16((Q₁/Q₂) from therelation of R₁<0.86R₂ because R₁ and R₂ are defined by R₁=ω₁L₁/Q₁ andR₂=ω₂L₂/Q₂, respectively. In addition, r₂ is greater than 1,500,preferably, 2,000.

The above-described quartz crystal resonators are formed by at least onemethod of chemical, mechanical and physical methods. The mechanicalmethod, for example, uses a particle such as GC#1000 and the physicalmethod, for example, uses atom or molecule. Therefore, these methods arecalled “a particle method” here. In addition, the present invention isnot limited to the resonators described above, but includes such apiezoelectric resonator for sensing pressure as a flexural mode, tuningfork resonator, a torsional mode resonator, a thickness shear moderesonator, SAW resonator and so on. In detail, there is a relationshipbetween the pressure and an oscillation frequency of the resonators or aseries resistance R₁ thereof. In more detail, the higher the pressurebecomes, the lower the oscillation frequency becomes or the higher theseries resistance R₁ becomes. Namely, since the oscillation frequency ofthe resonators or the series resistance thereof changes by a change ofthe pressure, the pressure is measured from the relationship.

Thus, the electronic apparatus of this invention comprising a displayportion and a quartz crystal oscillator at least may operate normallybecause the quartz crystal oscillator comprises the quartz crystaloscillating circuit with a high frequency stability, namely, a highfrequency reliability.

As described above, it will be easily understood that the electronicapparatus comprising the quartz crystal oscillator comprising the quartzcrystal oscillating circuit having the flexural mode, quartz crystaltuning fork resonator with novel shapes, the novel electrodeconstruction and excellent electrical characteristics, according to thepresent invention, may have the outstanding effects. Similar to this, itwill be easily understood that the electronic apparatus comprising thequartz crystal oscillator comprising the quartz crystal oscillatingcircuit having the length-extensional mode quartz crystal resonator withthe novel cutting angle and the novel shape, according to the presentinvention, may have also the outstanding effect. In addition to this,while the present invention has been shown and described with referenceto preferred embodiments thereof, it will be understood by those skilledin the art that the changes in shape and electrode construction can bemade therein without departing from the spirit and scope of the presentinvention.

1. A method for manufacturing a quartz crystal unit, comprising thesteps of: providing a quartz crystal wafer; providing a case having aninterior space and a lid; forming a quartz crystal tuning fork resonatorhaving an overall length capable of vibrating in a flexural mode of aninverse phase by etching the quartz crystal wafer to form a quartzcrystal tuning fork base, first and second quartz crystal tuning forktines connected to the quartz crystal tuning fork base, each of thefirst and second quartz crystal tuning fork tines having opposite mainsurfaces and opposite side surfaces, and at least one groove having alength formed in at least one of the opposite main surfaces of each ofthe first and second quartz crystal tuning fork tines, the quartzcrystal tuning fork resonator having a fundamental mode of vibration anda second overtone mode of vibration; determining the length of the atleast one groove formed in the at least one of the opposite mainsurfaces of each of the first and second quartz crystal tuning forktines and the overall length of the quartz crystal tuning fork resonatorso that a series resistance R₁ of the fundamental mode of vibration ofthe quartz crystal tuning fork resonator is less than a seriesresistance R₂ of the second overtone mode of vibration thereof;disposing an electrode on at least one of the opposite side surfaces ofeach of the first and second quartz crystal tuning fork tines so thatthe electrode disposed on the at least one of the opposite side surfacesof the first quartz crystal tuning fork tine has an electrical polarityopposite to an electrical polarity of the electrode disposed on the atleast one of the opposite side surfaces of the second quartz crystaltuning fork tine; housing the quartz crystal tuning fork resonator inthe interior space of the case; and connecting the lid to the case afterthe housing step.
 2. A method according to claim 1; wherein the oppositemain surfaces have a first main surface and a second main surface andthe opposite side surfaces have an inner side surface and an outer sidesurface, the inner side surface of the first quartz crystal tuning forktine confronting the inner side surface of the second quartz crystaltuning fork tine; wherein the quartz crystal wafer has a first surfaceand a second surface opposite the first surface; wherein the case has amounting portion in the interior space; and further comprising the stepsof disposing at least one first metal film on each of the first andsecond surfaces of the quartz crystal wafer; disposing a first resist onthe at least one first metal film disposed on each of the first andsecond surfaces of the quartz crystal wafer; removing the first resiston the at least one first metal film disposed on each of the first andsecond surfaces of the quartz crystal wafer and the at least one firstmetal film on each of the first and second surfaces of the quartzcrystal wafer to form a pattern of a tuning fork shape on each of thefirst and second surfaces of the quartz crystal wafer; forming thequartz crystal tuning fork base, and the first and second quartz crystaltuning fork tines in a first etching process; forming at least onegroove in at least one of the first and second main surfaces of each ofthe first and second quartz crystal tuning fork tines in a secondetching process different from the first etching process so that a widthW₂ of the at least one groove formed in the at least one of the firstand second main surfaces of each of the first and second quartz crystaltuning fork tines is greater than a distance W₁ in the width directionof the at least one groove measured from a first outer edge of the atleast one groove to a first outer edge of the corresponding one of thefirst and second quartz crystal tuning fork tines and a distance W₂ inthe width direction of the at least one groove measured from a secondouter edge opposite the first outer edge of the at least one groove to asecond outer edge opposite the first outer edge of the corresponding oneof the first and second quartz crystal tuning fork tines; disposing atleast one second metal film on each of the first and second mainsurfaces and the inner and outer side surfaces of each of the first andsecond quartz crystal tuning fork tines, and a surface of the at leastone groove formed in the at least one of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines; disposing a second resist on the at least one second metal filmdisposed on each of the first and second main surfaces and the inner andouter side surfaces of each of the first and second quartz crystaltuning fork tines, and the surface of the at least one groove formed inthe at least one of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines; forming a firstelectrode on the surface of the at least one groove formed in the atleast one of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines and a second electrode on eachof the inner and outer side surfaces of each of the first and secondquartz crystal tuning fork tines so that the first electrode formed onthe surface of the at least one groove formed in the at least one of thefirst and second main surfaces of the first quartz crystal tuning forktine is connected to the second electrode formed on each of the innerand outer side surfaces of the second quartz crystal tuning fork tine,and the first electrode formed on the surface of the at least one grooveformed in the at least one of the first and second main surfaces of thesecond quartz crystal tuning fork tine is connected to the secondelectrode formed on each of the inner and outer side surfaces of thefirst quartz crystal tuning fork tine; removing the second resist on theat least one second metal film disposed on each of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines; mounting the quartz crystal tuning fork resonator on the mountingportion in the interior space of the case; adjusting an oscillationfrequency of the quartz crystal tuning fork resonator; and connectingthe lid to the case after the mounting step.
 3. A method according toclaim 2; wherein the forming step of the at least one groove includesthe step of forming a groove having a first stepped portion and a secondstepped portion opposite the first stepped portion in the widthdirection, and a third stepped portion connecting the first steppedportion to the second stepped portion in each of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines in the second etching process different from the first etchingprocess; and further comprising the sequential steps of forming thequartz crystal tuning fork base, and the first and second quartz crystaltuning fork tines in the first etching process; and forming the groovehaving the first, second and third stepped portions in each of the firstand second main surfaces of each of the first and second quartz crystaltuning fork tines in the second etching process different from the firstetching process so that a width of the groove formed in each of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines is greater than a distance in the widthdirection of the groove measured from an outer edge of the groove to anouter edge of the corresponding one of the first and second quartzcrystal tuning fork tines.
 4. A method according to claim 3; wherein thestep of forming the quartz crystal tuning fork base, and the first andsecond quartz crystal tuning fork tines includes the steps of forming inthe quartz crystal wafer having a thickness in the range of 0.05 mm to0.18 mm a quartz crystal tuning fork shape having the quartz crystaltuning fork base, and the first and second quartz crystal tuning forktines in the first etching process and forming the quartz crystal tuningfork base having a first base portion including a first width W₅ and asecond base portion including a second width W₆ and a length l₄ greaterthan 0.03 mm and less than 0.48 mm so that two cut portions are formedbetween the first and second base portions of the quartz crystal tuningfork base, each of the first and second quartz crystal tuning fork tinesbeing connected to the first base portion of the quartz crystal tuningfork base; and wherein the step of forming the groove having the first,second and third stepped portions so that the width of the groove isgreater than the distance includes the step of forming the groove havingthe first, second and third stepped portions in each of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines in the second etching process different from the firstetching process so that a spaced-apart distance between the first andsecond quartz crystal tuning fork tines is greater than the width of thegroove formed in each of the first and second main surfaces of each ofthe first and second quartz crystal tuning fork tines and is within arange of 0.05 mm to 0.35 mm, and the width W₂ of the groove formed ineach of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines is within a range of 0.03 mm to0.12 mm and a length of the groove formed in each of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines is within a range of 0.32 mm to 1.1 mm.
 5. A methodaccording to claim 2; wherein the step of forming the quartz crystaltuning fork base, and the first and second quartz crystal tuning forktines is performed before the step of forming the at least one groove inthe at least one of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines; wherein the formingstep of the at least one groove includes the steps of forming a groovein each of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines in the second etching processdifferent from the first etching process so that a depth of the grooveformed in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines is greater than 0.025mm and the oscillation frequency of the quartz crystal tuning forkresonator is in the range of 32.78 kHz to 34.9 kHz; and furthercomprising the steps of forming a metal film on at least one of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines after the forming step of the first and secondelectrodes and before the mounting step so that the oscillationfrequency of the quartz crystal tuning fork resonator is lower than32.73 kHz; and adjusting the oscillation frequency of the quartz crystaltuning fork resonator after the mounting step so that the oscillationfrequency of the quartz crystal tuning fork resonator is about 32.768kHz with a frequency deviation within a range of −100 ppm to +100 ppm.6. A method according to claim 2; further comprising the sequentialsteps of removing the first resist on the at least one first metal filmdisposed on each of the first and second surfaces of the quartz crystalwafer and the at least one first metal film on each of the first andsecond surfaces of the quartz crystal wafer to form the pattern of thetuning fork shape having a tuning fork base, and first and second tuningfork tines each not having a through-hole on each of the first andsecond surfaces of the quartz crystal wafer; forming the first andsecond quartz crystal tuning fork tines each not having a through-hole;and forming a groove having a first side surface opposite the inner sidesurface and a second side surface opposite the outer side surface, and athird side surface connecting the first side surface to the second sidesurface in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines so that a width of thegroove formed in each of the first and second main surfaces of each ofthe first and second quartz crystal tuning fork tines is greater than adistance in the width direction of the groove measured from an outeredge of the groove to an outer edge of the corresponding one of thefirst and second quartz crystal tuning fork tines; wherein the case hasan open end; and further comprising the steps of removing the firstresist on the at least one first metal film disposed on each of thefirst and second surfaces of the quartz crystal wafer before thedisposing step of the at least one second metal film; removing thesecond resist on the at least one second metal film disposed on each ofthe first and second main surfaces of each of the first and secondquartz crystal tuning fork tines before the mounting step; andconnecting the lid to the case to cover the open end thereof after themounting step.
 7. A method according to claim 6; further comprising thestep of forming the quartz crystal tuning fork base having a first baseportion including a first width W₅ and a second base portion including asecond width W₆ greater than or equal to the first width W₅, and alength l₄ greater than 0.03 mm and less than 0.48 mm so that two cutportions are formed between the first and second base portions of thequartz crystal tuning fork base, each of the first and second quartzcrystal tuning fork tines being connected to the first base portion ofthe quartz crystal tuning fork base.
 8. A method according to claim 2;wherein the quartz crystal tuning fork resonator has a parabolic curvein frequency-temperature behavior; and further comprising the sequentialsteps of forming the at least one groove in each of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines in the second etching process different from the first etchingprocess so that the oscillation frequency of the quartz crystal tuningfork resonator has a first oscillation frequency and the quartz crystaltuning fork resonator has a turning point in the frequency-temperaturebehavior; forming a metal film on at least one of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines after the forming step of the first and second electrodes andbefore the mounting step so that the oscillation frequency of the quartzcrystal tuning fork resonator has a second oscillation frequency;trimming the metal film formed on the at least one of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines before the mounting step so that the oscillationfrequency of the quartz crystal tuning fork resonator has a thirdoscillation frequency; and trimming the metal film formed on the atleast one of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines after the mounting step so thatthe oscillation frequency of the quartz crystal tuning fork resonatorhas a fourth oscillation frequency.
 9. A method according to claim 8;wherein the forming step of the at least one groove includes the step offorming the at least one groove in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines in the second etching process different from the first etchingprocess so that a depth of the at least one groove formed in each of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines is greater than 0.025 mm; wherein the firstoscillation frequency is in the range of 32.78 kHz to 34.9 kHz; whereinthe turning point of the quartz crystal tuning fork resonator is in therange of 15° C. to 35° C.; wherein the second oscillation frequency islower than 32.73 kHz; wherein the third oscillation frequency is about32.768 kHz with a frequency deviation within a range of −9000 ppm to+100 ppm; and wherein the fourth oscillation frequency is about 32.768kHz with a frequency deviation within a range of −100 ppm to +100 ppm.10. A method according to claim 1; wherein the opposite main surfaceshave a first main surface and a second main surface and the oppositeside surfaces have an inner side surface and an outer side surface, theinner side surface of the first quartz crystal tuning fork tineconfronting the inner side surface of the second quartz crystal tuningfork tine; wherein the quartz crystal wafer has a first surface and asecond surface opposite the first surface; wherein the case has amounting portion in the interior space; and further comprising thesequential steps of disposing at least one first metal film on each ofthe first and second surfaces of the quartz crystal wafer; disposing afirst resist on the at least one first metal film disposed on each ofthe first and second surfaces of the quartz crystal wafer; removing thefirst resist on the at least one first metal film disposed on each ofthe first and second surfaces of the quartz crystal wafer and the atleast one first metal film on each of the first and second surfaces ofthe quartz crystal wafer to form a pattern of a tuning fork shape oneach of the first and second surfaces of the quartz crystal wafer;forming in the quartz crystal wafer the quartz crystal tuning fork base,and the first and second quartz crystal tuning fork tines; forming atleast one groove having a first side surface opposite the inner sidesurface and a second side surface opposite the outer side surface, and athird side surface connecting the first side surface to the second sidesurface in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines so that a width of theat least one groove formed in each of the first and second main surfacesof each of the first and second quartz crystal tuning fork tines isgreater than a distance in the width direction of the at least onegroove measured from an outer edge of the at least one groove to anouter edge of the corresponding one of the first and second quartzcrystal tuning fork tines; disposing at least one second metal film oneach of the first and second main surfaces and the inner and outer sidesurfaces of each of the first and second quartz crystal tuning forktines, and each of the first and second side surfaces of the at leastone groove formed in each of the first and second main surfaces of eachof the first and second quartz crystal tuning fork tines; disposing asecond resist on the at least one second metal film disposed on each ofthe first and second main surfaces and the inner and outer side surfacesof each of the first and second quartz crystal tuning fork tines, andeach of the first and second side surfaces of the at least one grooveformed in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines; forming a firstelectrode on each of the first and second side surfaces of the at leastone groove formed in each of the first and second main surfaces of eachof the first and second quartz crystal tuning fork tines and a secondelectrode on each of the inner and outer side surfaces of each of thefirst and second quartz crystal tuning fork tines so that the firstelectrode formed on each of the first and second side surfaces of the atleast one groove formed in each of the first and second main surfaces ofthe first quartz crystal tuning fork tine is connected to the secondelectrode formed on each of the inner and outer side surfaces of thesecond quartz crystal tuning fork tine, and the first electrode formedon each of the first and second side surfaces of the at least one grooveformed in each of the first and second main surfaces of the secondquartz crystal tuning fork tine is connected to the second electrodeformed on each of the inner and outer side surfaces of the first quartzcrystal tuning fork tine; mounting the quartz crystal tuning forkresonator on the mounting portion in the interior space of the case; andconnecting the lid to the case after the mounting step.
 11. A methodaccording to claim 10; wherein the quartz crystal tuning fork resonatorhas an oscillation frequency; and further comprising the step of formingthe at least one groove in each of the first and second main surfaces ofeach of the first and second quartz crystal tuning fork tines so that adepth of the at least one groove formed in each of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines is greater than 0.025 mm and the oscillation frequency of thequartz crystal tuning fork resonator is in the range of 32.78 kHz to34.9 kHz.
 12. A method according to claim 10; wherein the quartz crystaltuning fork resonator has an oscillation frequency; and furthercomprising the step of forming a metal film on at least one of the firstand second main surfaces of each of the first and second quartz crystaltuning fork tines after the forming step of the first and secondelectrodes and before the mounting step so that the oscillationfrequency of the quartz crystal tuning fork resonator is lower than32.73 kHz.
 13. A method according to claim 10; wherein the quartzcrystal tuning fork resonator has an oscillation frequency; wherein thecase has a through-hole; and further comprising the steps of removingthe second resists disposed on the second metal films before themounting step; disposing a metal or a glass into the through-hole of thecase to close the through-hole in a vacuum; and adjusting in a vacuumthe oscillation frequency of the quartz crystal tuning fork resonatorafter the connecting step of the lid and the case and before thedisposing step of the metal or the glass.
 14. A method according toclaim 10; wherein the quartz crystal tuning fork resonator has anoscillation frequency; wherein the case has a through-hole; and furthercomprising the steps of removing the second resists disposed on thesecond metal films before the mounting step; disposing a metal or aglass into the through-hole of the case to close the through-hole in avacuum after the connecting step of the lid and the case; and adjustingthe oscillation frequency of the quartz crystal tuning fork resonatorafter the disposing step of the metal or the glass so that theoscillation frequency is about 32.768 kHz with a frequency deviationwithin a range of −50 ppm to +50 ppm.
 15. A method according to claim10; wherein the quartz crystal tuning fork resonator has an oscillationfrequency; wherein the case has no through-hole and an open end; whereinthe connecting step of the lid and the case includes the step ofconnecting the lid to the case to cover the open end of the case in avacuum; and further comprising the steps of removing the second resistsdisposed on the second metal films before the mounting step; adjustingthe oscillation frequency of the quartz crystal tuning fork resonatorafter the mounting step and before the connecting step of the lid andthe case so that the oscillation frequency of the quartz crystal tuningfork resonator is about 32.768 kHz with a frequency deviation within arange of −100 ppm to +100 ppm.
 16. A method according to claim 10;further comprising the steps of forming the at least one groove in eachof the first and second main surfaces of each of the first and secondquartz crystal tuning fork tines so that a spaced-apart distance betweenthe first and second quartz crystal tuning fork tines is greater thanthe width of the at least one groove formed in each of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines and is within a range of 0.05 mm to 0.35 mm, and thewidth of the at least one groove formed in each of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines is within a range of 0.03 mm to 0.12 mm; and forming the quartzcrystal tuning fork base having a first base portion including a firstwidth W₅ and a second base portion including a second width W₆ greaterthan or equal to the first width W₅ and a length l₄ greater than 0.03 mmand less than 0.48 mm so that two cut portions are formed between thefirst and second base portions of the quartz crystal tuning fork base,each of the first and second quartz crystal tuning fork tines beingconnected to the first base portion of the quartz crystal tuning forkbase.
 17. A method according to claim 10; wherein the quartz crystaltuning fork resonator has an oscillation frequency; and furthercomprising the steps of forming a metal film on at least one of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines after the forming step of the first and secondelectrodes and before the mounting step so that the oscillationfrequency of the quartz crystal tuning fork resonator has a firstoscillation frequency; adjusting the oscillation frequency of the quartzcrystal tuning fork resonator by trimming the metal film formed on theat least one of the first and second main surfaces of each of the firstand second quartz crystal tuning fork tines before the mounting step sothat the oscillation frequency of the quartz crystal tuning forkresonator has a second oscillation frequency; and adjusting theoscillation frequency of the quartz crystal tuning fork resonator afterthe mounting step so that the oscillation frequency of the quartzcrystal tuning fork resonator has a third oscillation frequency.
 18. Amethod according to claim 17; wherein the first oscillation frequency islower than 32.73 kHz; wherein the second oscillation frequency is about32.768 kHz with a frequency deviation within a range of −9000 ppm to+100 ppm; and wherein the third oscillation frequency is about 32.768kHz with a frequency deviation within a range of −100 ppm to +100 ppm.19. A method according to claim 10; wherein the forming step of the atleast one groove includes the step of forming a plurality of groovesdivided in the length direction in at least one of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines in the second etching process different from the first etchingprocess so that a spaced-apart distance between the first and secondquartz crystal tuning fork tines is greater than a width of at least oneof the grooves formed in the at least one of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines and the width of the at least one of the grooves formed in the atleast one of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines is within a range of 0.03 mm to0.12 mm.
 20. A method according to claim 10; wherein the quartz crystaltuning fork resonator has an oscillation frequency and a parabolic curvein frequency-temperature behaviour; and further comprising the steps offorming the at least one groove in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines so that the oscillation frequency of the quartz crystal tuningfork resonator has a first oscillation frequency and the quartz crystaltuning fork resonator has a turning point; forming a metal film on atleast one of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines after the forming step of thefirst and second electrodes and before the mounting step so that theoscillation frequency of the quartz crystal tuning fork resonator has asecond oscillation frequency; adjusting the oscillation frequency of thequartz crystal tuning fork resonator by trimming the metal film formedon the at least one of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines before the mountingstep so that the oscillation frequency of the quartz crystal tuning forkresonator has a third oscillation frequency; and adjusting theoscillation frequency of the quartz crystal tuning fork resonator afterthe mounting step so that the oscillation frequency of the quartzcrystal tuning fork resonator has a fourth oscillation frequency.
 21. Amethod according to claim 20; wherein the first oscillation frequency isin the range of 32.78 kHz to 34.9 kHz and the turning point is in therange of 15° C. to 35° C.; wherein the second oscillation frequency islower than 32.73 kHz; wherein the third oscillation frequency is about32.768 kHz with a frequency deviation within a range of −9000 ppm to+100 ppm; and wherein the fourth oscillation frequency is about 32.768kHz with a frequency deviation within a range of −100 ppm to +100 ppm.22. A method according to claim 10; further comprising the step offorming the quartz crystal tuning fork base having a length l₂, and afirst base portion including a first width W₅ and a second base portionincluding a second width W₆ and a length l₄ so that two cut portions areformed between the first and second base portions of the quartz crystaltuning fork base and the length l₄ is less than or equal to a length l₅,the length l₅ being defined by l₅=l₂−l₄; wherein each of the first andsecond quartz crystal tuning fork tines is connected to the first baseportion of the quartz crystal tuning fork base; wherein the second baseportion of the quartz crystal tuning fork base has a first side surfaceand a second side surface opposite the first side surface; wherein afirst frame portion protrudes from the first side surface of the secondbase portion of the quartz crystal tuning fork base and a second frameportion protrudes from the second side surface of the second baseportion of the quartz crystal tuning fork base, each of the first andsecond frame portions extending in a common direction with the first andsecond quartz crystal tuning fork tines outside the first and secondquartz crystal tuning fork tines; and wherein the length l₄ is greaterthan 0.03 mm and less than 0.48 mm.
 23. A method according to claim 1;wherein the disposing step of the electrode includes the step ofdisposing an electrode on a surface of the at least one groove formed inthe at least one of the opposite main surfaces of each of the first andsecond quartz crystal tuning fork tines so that the electrode disposedon the surface of the at least one groove formed in the at least one ofthe opposite main surfaces of the first quartz crystal tuning fork tinehas an electrical polarity opposite to an electrical polarity of theelectrode disposed on the surface of the at least one groove formed inthe at least one of the opposite main surfaces of the second quartzcrystal tuning fork tine; wherein the quartz crystal tuning forkresonator has a piezoelectric constant e′₁₂ to drive the quartz crystaltuning fork resonator; wherein the quartz crystal wafer has a cuttingangle; and further comprising the step of determining the cutting angleof the quartz crystal wafer, a dimension of the at least one grooveformed in the at least one of the opposite main surfaces of each of thefirst and second quartz crystal tuning fork tines, and a dimension ofthe electrode disposed on the surface of the at least one groove formedin the at least one of the opposite main surfaces of each of the firstand second quartz crystal tuning fork tines so that the piezoelectricconstant e′₁₂ of the quartz crystal tuning fork resonator is within arange of 0.12 C/m² to 0.19 C/m² in the absolute value.
 24. A methodaccording to claim 1; wherein the quartz crystal tuning fork resonatorhas a merit value M₁ of the fundamental mode of vibration and a meritvalue M₂ of the second overtone mode of vibration, the merit value M₁being defined by the ratio (Q₁/r₁) and the merit value M₂ being definedby the ratio (Q₂/r₂), where Q₁ and Q₂ represent a quality factor of thefundamental mode of vibration and the second overtone mode of vibration,respectively, of the quartz crystal tuning fork resonator and r₁ and r₂represent a capacitance ratio of the fundamental mode of vibration andthe second overtone mode of vibration, respectively, of the quartzcrystal tuning fork resonator; wherein the opposite main surfaces have afirst main surface and a second main surface; and further comprising thesteps of forming a quartz crystal tuning fork shape having the quartzcrystal tuning fork base, and the first and second quartz crystal tuningfork tines; forming a groove in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines; forming an electrode on a surface of the groove formed in each ofthe first and second main surfaces of each of the first and secondquartz crystal tuning fork tines so that the electrode formed on thesurface of the groove formed in each of the first and second mainsurfaces of the first quartz crystal tuning fork tine has an electricalpolarity opposite to an electrical polarity of the electrode formed onthe surface of the groove formed in each of the first and second mainsurfaces of the second quartz crystal tuning fork tine, each of thequartz crystal tuning fork shape, the groove formed in each of the firstand second main surfaces of each of the first and second quartz crystaltuning fork tines and the electrode formed on the surface of the grooveformed in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines having a dimension;and determining the dimension of each of the quartz crystal tuning forkshape, the groove formed in each of the first and second main surfacesof each of the first and second quartz crystal tuning fork tines and theelectrode formed on the surface of the groove formed in each of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines so that the merit value M₁ of the fundamentalmode of vibration of the quartz crystal tuning fork resonator is greaterthan the merit value M₂ of the second overtone mode of vibrationthereof.
 25. A method according to claim 1; wherein the opposite mainsurfaces have a first main surface and a second main surface and theopposite side surfaces have an inner side surface and an outer sidesurface, the inner side surface of the first quartz crystal tuning forktine confronting the inner side surface of the second quartz crystaltuning fork tine; wherein the quartz crystal wafer has a first surfaceand a second surface opposite the first surface; wherein the case has amounting portion in the interior space; and further comprising thesequential steps of disposing at least one first metal film on each ofthe first and second surfaces of the quartz crystal wafer; disposing afirst resist on the at least one first metal film disposed on each ofthe first and second surfaces of the quartz crystal wafer; removing thefirst resist on the at least one first metal film disposed on each ofthe first and second surfaces of the quartz crystal wafer and the atleast one first metal film on each of the first and second surfaces ofthe quartz crystal wafer to form a pattern of a tuning fork shape oneach of the first and second surfaces of the quartz crystal wafer;forming simultaneously in the quartz crystal wafer the quartz crystaltuning fork base and the first and second quartz crystal tuning forktines, and at least one groove in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines; disposing at least one second metal film on each of the first andsecond main surfaces and the inner and outer side surfaces of each ofthe first and second quartz crystal tuning fork tines, and a surface ofthe at least one groove formed in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines; disposing a second resist on the at least one second metal filmdisposed on each of the first and second main surfaces and the inner andouter side surfaces of each of the first and second quartz crystaltuning fork tines, and the surface of the at least one groove formed ineach of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines; forming a first electrode onthe surface of the at least one groove formed in each of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines and a second electrode on each of the inner and outerside surfaces of each of the first and second quartz crystal tuning forktines so that the first electrode formed on the surface of the at leastone groove formed in each of the first and second main surfaces of thefirst quartz crystal tuning fork tine is connected to the secondelectrode formed on each of the inner and outer side surfaces of thesecond quartz crystal tuning fork tine, and the first electrode formedon the surface of the at least one groove formed in each of the firstand second main surfaces of the second quartz crystal tuning fork tineis connected to the second electrode formed on each of the inner andouter side surfaces of the first quartz crystal tuning fork tine;mounting the quartz crystal tuning fork resonator on the mountingportion in the interior space of the case; and connecting the lid to thecase after the mounting step.
 26. A method for manufacturing anelectronic apparatus, comprising manufacturing a quartz crystal unitaccording to claim 1; and mounting the quartz crystal unit in anelectronic apparatus to drive an element of the electronic apparatus.27. A method according to claim 26; wherein the opposite main surfaceshave a first main surface and a second main surface and the oppositeside surfaces have an inner side surface and an outer side surface, theinner side surface of the first quartz crystal tuning fork tineconfronting the inner side surface of the second quartz crystal tuningfork tine; wherein the quartz crystal wafer has a first surface and asecond surface opposite the first surface; wherein the case has amounting portion in the interior space; wherein the step ofmanufacturing the quartz crystal unit includes the sequential steps ofdisposing at least one first metal film on each of the first and secondsurfaces of the quartz crystal wafer; disposing a first resist on the atleast one first metal film disposed on each of the first and secondsurfaces of the quartz crystal wafer; removing the first resist on theat least one first metal film disposed on each of the first and secondsurfaces of the quartz crystal wafer and the at least one first metalfilm on each of the first and second surfaces of the quartz crystalwafer to form a pattern of a tuning fork shape on each of the first andsecond surfaces of the quartz crystal wafer; forming in the quartzcrystal wafer the quartz crystal tuning fork base, and the first andsecond quartz crystal tuning fork tines; forming a groove in each of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines so that a width of the groove formed in eachof the first and second main surfaces of each of the first and secondquartz crystal tuning fork tines is greater than a distance in the widthdirection of the groove measured from an outer edge of the groove to anouter edge of the corresponding one of the first and second quartzcrystal tuning fork tines; disposing at least one second metal film oneach of the first and second main surfaces and the inner and outer sidesurfaces of each of the first and second quartz crystal tuning forktines, and a surface of the groove formed in each of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines; disposing a second resist on the at least one secondmetal film disposed on each of the first and second main surfaces andthe inner and outer side surfaces of each of the first and second quartzcrystal tuning fork tines, and the surface of the groove formed in eachof the first and second main surfaces of each of the first and secondquartz crystal tuning fork tines; forming a first electrode on thesurface of the groove formed in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines and a second electrode on each of the inner and outer sidesurfaces of each of the first and second quartz crystal tuning forktines so that the first electrode formed on the surface of the grooveformed in each of the first and second main surfaces of the first quartzcrystal tuning fork tine is connected to the second electrode formed oneach of the inner and outer side surfaces of the second quartz crystaltuning fork tine, and the first electrode formed on the surface of thegroove formed in each of the first and second main surfaces of thesecond quartz crystal tuning fork tine is connected to the secondelectrode formed on each of the inner and outer side surfaces of thefirst quartz crystal tuning fork tine; removing the second resist on theat least one second metal film disposed on each of the first and secondmain surfaces and the inner and outer side surfaces of each of the firstand second quartz crystal tuning fork tines, and the surface of thegroove formed in each of the first and second main surfaces of each ofthe first and second quartz crystal tuning fork tines; mounting thequartz crystal tuning fork resonator on the mounting portion in theinterior space of the case; and connecting the lid to the case after themounting step.
 28. A method according to claim 27; wherein the quartzcrystal tuning fork resonator has an oscillation frequency; and whereinthe step of manufacturing the quartz crystal unit includes the steps offorming in the quartz crystal wafer having a thickness in the range of0.05 mm to 0.18 mm the quartz crystal tuning fork base, and the firstand second quartz crystal tuning fork tines; forming the groove in eachof the first and second main surfaces of each of the first and secondquartz crystal tuning fork tines so that a spaced-apart distance betweenthe first and second quartz crystal tuning fork tines is greater thanthe width of the groove formed in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines and is within a range of 0.05 mm to 0.35 mm, and the width of thegroove formed in each of the first and second main surfaces of each ofthe first and second quartz crystal tuning fork tines is within a rangeof 0.03 mm to 0.12 mm; adjusting the oscillation frequency of the quartzcrystal tuning fork resonator after the first and second electrodes andbefore the mounting step so that the oscillation frequency of the quartzcrystal tuning fork resonator is about 32.768 kHz with a frequencydeviation within a range of −9000 ppm to +5000 ppm and adjusting theoscillation frequency of the quartz crystal tuning fork resonator afterthe mounting step so that the oscillation frequency of the quartzcrystal tuning fork resonator is about 32.768 kHz with a frequencydeviation within a range of −100 ppm to +100 ppm.
 29. A method accordingto claim 26; wherein the electronic apparatus has a display portion anda CPU; and further comprising the steps of providing a first quartzcrystal oscillator comprised of a first quartz crystal oscillatingcircuit and a second quartz crystal oscillator comprised of a secondquartz crystal oscillating circuit, each of the first and second quartzcrystal oscillating circuits having an amplifier, at least one resistor,and a plurality of capacitors; and arranging the first and second quartzcrystal oscillators in the electronic apparatus having the displayportion and the CPU so that the first quartz crystal oscillating circuitcomprises the quartz crystal unit having the quartz crystal tuning forkresonator electrically connected to the amplifier, the capacitors andthe at least one resistor, and an output signal of the first quartzcrystal oscillating circuit is a clock signal for use in operation ofthe electronic apparatus to display time information at the displayportion of the electronic apparatus; and so that the second quartzcrystal oscillating circuit comprises a length-extensional mode quartzcrystal resonator or a thickness shear mode quartz crystal resonator,and an output signal of the second quartz crystal oscillating circuit isa clock signal for use in operation of the electronic apparatus tooperate the CPU of the electronic apparatus; wherein the quartz crystaltuning fork resonator has a merit value M₁ of the fundamental mode ofvibration and a merit value M₂ of the second overtone mode of vibration,the merit value M₁ being defined by the ratio (Q₁/r₁) and the meritvalue M₂ being defined by the ratio (Q₂/r₂), where Q₁ and Q₂ represent aquality factor of the fundamental mode of vibration and the secondovertone mode of vibration, respectively, of the quartz crystal tuningfork resonator and r₁ and r₂ represent a capacitance ratio of thefundamental mode of vibration and the second overtone mode of vibration,respectively, of the quartz crystal tuning fork resonator; wherein theopposite main surfaces have a first main surface and a second mainsurface; and wherein the step of manufacturing the quartz crystal unitincludes the steps of forming a quartz crystal tuning fork shape havingthe quartz crystal tuning fork base, and the first and second quartzcrystal tuning fork tines; forming a groove in at least one of the firstand second main surfaces of each of the first and second quartz crystaltuning fork tines; forming an electrode on a surface of the grooveformed in the at least one of the first and second main surfaces of eachof the first and second quartz crystal tuning fork tines so that theelectrode formed on the surface of the groove formed in the at least oneof the first and second main surfaces of the first quartz crystal tuningfork tine has an electrical polarity opposite to an electrical polarityof the electrode formed on the surface of the groove formed in the atleast one of the first and second main surfaces of the second quartzcrystal tuning fork tine, each of the quartz crystal tuning fork shape,the groove formed in the at least one of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines and the electrode formed on the surface of the groove formed inthe at least one of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines having a dimension;and determining the dimension of each of the quartz crystal tuning forkshape, the groove formed in the at least one of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines and the electrode formed on the surface of the groove formed inthe at least one of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines so that the meritvalue M₁ of the fundamental mode of vibration of the quartz crystaltuning fork resonator is greater than the merit value M₂ of the secondovertone mode of vibration thereof and the merit value M₂ of the secondovertone mode of vibration is less than
 30. 30. A method according toclaim 29; wherein the forming step of the quartz crystal tuning forkshape is performed before the forming step of the groove; and furthercomprising the step of forming the quartz crystal tuning fork basehaving a first base portion including a first width W₅ and a second baseportion including a second width W₆ greater than or equal to the firstwidth W₅, and a length l₄ greater than 0.03 mm and less than 0.48 mm sothat two cut portions are formed between the first and second baseportions of the quartz crystal tuning fork base, each of the first andsecond quartz crystal tuning fork tines being connected to the firstbase portion of the quartz crystal tuning fork base; wherein the quartzcrystal tuning fork resonator has an oscillation frequency; and furthercomprising the step of forming the groove in the at least one of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines so that a depth of the groove formed in the atleast one of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines is in the range of 0.025 mm to0.075 mm and the oscillation frequency of the quartz crystal tuning forkresonator is in the range of 32.78 kHz to 34.9 kHz.
 31. A methodaccording to claim 26; wherein the electronic apparatus has a displayportion and a CPU; and further comprising the steps of providing a firstquartz crystal oscillator comprised of a first quartz crystaloscillating circuit and a second quartz crystal oscillator comprised ofa second quartz crystal oscillating circuit, each of the first andsecond quartz crystal oscillating circuits having an amplifier, at leastone resistor, and a plurality of capacitors; and arranging the first andsecond quartz crystal oscillators in the electronic apparatus having thedisplay portion and the CPU so that the first quartz crystal oscillatingcircuit comprises the quartz crystal unit having the quartz crystaltuning fork resonator electrically connected to the amplifier, thecapacitors and the at least one resistor, and an output signal of thefirst quartz crystal oscillating circuit is a clock signal for use inoperation of the electronic apparatus to display time information at thedisplay portion of the electronic apparatus; and so that the secondquartz crystal oscillating circuit comprises a length-extensional modequartz crystal resonator or a thickness shear mode quartz crystalresonator, and an output signal of the second quartz crystal oscillatingcircuit is a clock signal for use in operation of the electronicapparatus to operate the CPU of the electronic apparatus; wherein thequartz crystal tuning fork resonator has a capacitance ratio r₁ of thefundamental mode of vibration and a capacitance ratio r₂ of the secondovertone mode of vibration, wherein the opposite main surfaces have afirst main surface and a second main surface; wherein the case has amounting portion in the interior space and an open end; and wherein thestep of manufacturing the quartz crystal unit includes the steps offorming a quartz crystal tuning fork shape having the quartz crystaltuning fork base, and the first and second quartz crystal tuning forktines; forming a groove in each of the first and second main surfaces ofeach of the first and second quartz crystal tuning fork tines; formingan electrode on a surface of the groove formed in each of the first andsecond main surfaces of each of the first and second quartz crystaltuning fork tines so that the electrode formed on the surface of thegroove formed in each of the first and second main surfaces of the firstquartz crystal tuning fork tine has an electrical polarity opposite toan electrical polarity of the electrode formed on the surface of thegroove formed in each of the first and second main surfaces of thesecond quartz crystal tuning fork tine; mounting the quartz crystaltuning fork resonator on the mounting portion in the interior space ofthe case; connecting the lid to the case to cover the open end of thecase, each of the quartz crystal tuning fork shape, the groove formed ineach of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines and the electrode formed on thesurface of the groove formed in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines having a dimension; and determining the dimension of each of thequartz crystal tuning fork shape, the groove formed in each of the firstand second main surfaces of each of the first and second quartz crystaltuning fork tines and the electrode formed on the surface of the grooveformed in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines so that thecapacitance ratio r₁ of the fundamental mode of vibration of the quartzcrystal tuning fork resonator is less than the capacitance ratio r₂ ofthe second overtone mode of vibration thereof and the capacitance ratior₂ of the second overtone mode of vibration is greater than
 1500. 32. Amethod according to claim 31; wherein the quartz crystal tuning forkresonator has an oscillation frequency; and further comprising the stepsof forming the groove in each of the first and second main surfaces ofeach of the first and second quartz crystal tuning fork tines so that adepth of the groove formed in each of the first and second main surfacesof each of the first and second quartz crystal tuning fork tines is inthe range of 0.03 mm to 0.055 mm and the oscillation frequency of thequartz crystal tuning fork resonator is in the range of 32.78 kHz to34.9 kHz; forming a metal film on at least one of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines after the forming step of the electrode and before the mountingstep so that the oscillation frequency of the quartz crystal tuning forkresonator is lower than 32.73 kHz; and adjusting the oscillationfrequency of the quartz crystal tuning fork resonator so that theoscillation frequency of the quartz crystal tuning fork resonator isabout 32.768 kHz with a frequency deviation within a range of −100 ppmto +100 ppm by trimming the metal film formed on the at least one of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines after the mounting step.
 33. A quartz crystalunit manufactured according to the method of claim
 1. 34. A unitaccording to claim 33; wherein the quartz crystal tuning fork resonatorhas a merit value M₁ of the fundamental mode of vibration and a meritvalue M₂ of the second overtone mode of vibration, the merit value M₁being defined by the ratio (Q₁/r₁) and the merit value M₂ being definedby the ratio (Q₂/r₂), where Q₁ and Q₂ represent a quality factor of thefundamental mode of vibration and the second overtone mode of vibration,respectively, of the quartz crystal tuning fork resonator and r₁ and r₂represent a capacitance ratio of the fundamental mode of vibration andthe second overtone mode of vibration, respectively, of the quartzcrystal tuning fork resonator; wherein the opposite main surfaces have afirst main surface and a second main surface; wherein a quartz crystaltuning fork shape has the quartz crystal tuning fork base, and the firstand second quartz crystal tuning fork tines and a groove is formed ineach of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines; wherein an electrode is formedon a surface of the groove formed in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines so that the electrode formed on the surface of the groove formedin each of the first and second main surfaces of the first quartzcrystal tuning fork tine has an electrical polarity opposite to anelectrical polarity of the electrode formed on the surface of the grooveformed in each of the first and second main surfaces of the secondquartz crystal tuning fork tine, each of the quartz crystal tuning forkshape, the groove formed in each of the first and second main surfacesof each of the first and second quartz crystal tuning fork tines and theelectrode formed on the surface of the groove formed in each of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines having a dimension; and wherein the dimensionof each of the quartz crystal tuning fork shape, the groove formed ineach of the first and second main surfaces of each of the first andsecond quartz crystal tuning fork tines and the electrode formed on thesurface of the groove formed in each of the first and second mainsurfaces of each of the first and second quartz crystal tuning forktines is determined so that the merit value M₁ of the fundamental modeof vibration of the quartz crystal tuning fork resonator is greater thanthe merit value M₂ of the second overtone mode of vibration thereof. 35.A unit according to claim 34; wherein the quartz crystal wafer has athickness in the range of 0.05 mm to 0.18 mm; wherein a spaced-apartdistance W₄ between the first and second quartz crystal tuning forktines is greater than a width W₂ of the groove formed in each of thefirst and second main surfaces of each of the first and second quartzcrystal tuning fork tines and is within a range of 0.05 mm to 0.35 mm,and the width W₂ of the groove formed in each of the first and secondmain surfaces of each of the first and second quartz crystal tuning forktines is within a range of 0.03 mm to 0.12 mm and a length of the grooveformed in each of the first and second main surfaces of each of thefirst and second quartz crystal tuning fork tines is within a range of0.32 mm to 1.1 mm; and wherein the quartz crystal tuning fork base has afirst base portion including a first width W₅ and a second base portionincluding a second width W₆ greater than or equal to the first width W₅,and a length l₄ greater than 0.03 mm and less than 0.48 mm so that twocut portions are formed between the first and second base portions ofthe quartz crystal tuning fork base, each of the first and second quartzcrystal tuning fork tines being connected to the first base portion ofthe quartz crystal tuning fork base.